It's U.S. Open time once again, and when the tennis swings into action next week, Novak Djokovic and Sam Stosur will be in New York as your defending champions.

Djokovic has not been able to reproduce the magic that was his 2011 season, and has subsequently been replaced atop the rankings by a most-familiar face/foe ... in Roger Federer.

The Serbian star still holds two of the four Grand Slams titles, but has been showing cracks in the armor.

Federer has been the best player on the men's tour in recent months, as evidenced by a men's-record-tying seventh Wimbledon title last month, a trip into the gold-medal match at the Olympic Games in London, and a record fifth Cincinnati Masters title last week when he straight-setted Djokovic in a marquee 1-versus-2 finale at the Western & Southern Open. With that victory, Federer equaled Rafael Nadal for the most-ever ATP Masters titles (21) in his storied career.

Note: The incomparable Federer has now won seven different tournaments at least five times.

The iconic Federer, of course, is the men's all-time Grand Slam king with 17 titles, including five U.S. Opens. He reached six straight finals in Flushing Meadows before settling for back-to-back semifinal losses in 2010 and 2011. The Swiss legend hasn't won it all in the Big Apple since 2008. One more big victory there would make him the Open Era king of New York, breaking a tie with American greats Jimmy Connors and Pete Sampras.

FYI: Americans William Larned, Dick Sears and Bill Tilden won the U.S. National Championships seven times apiece in the years ranging from 1881-1929. The Philadelphia native Tilden nailed down a whopping six straight from 1920-25.

Moving on.

The women's top seed in Flushing will be Aussie Open champ Victoria Azarenka, but she, like Stosur, is not the experts' pick to run the table at the $22 million fortnight.

The top-ranked women in the world right now are Azarenka and Wimbledon runner- up Agnieszka Radwanska, but the true cream of the crop has to be Wimbledon champion and Olympic gold medalist Serena Williams and French Open titlist Maria Sharapova (who, by the way, launched a new candy business, Sugarpova, on Monday).

Serena has appeared in three of tennis' last five really big events, which includes the Summer Games in London, and has won the last two -- Wimbledon and the Olympics, both at the All England Club.

Meanwhile, the 2006 U.S. Open champion Sharapova has appeared in no less than three of the last five Grand Slam finals, including a victory at the French Open that produced a career Grand Slam for the tall Russian.

Serena and her fellow former No. 1 Sharapova clashed in the gold-medal match in London a few weeks ago with a career Golden Slam awaiting the winner, which turned out to be the powerful American, in a big way, on the grass at the famed Centre Court.

The 30-year-old Serena leads all active women (by a wide margin) with 14 major titles, including a trio of U.S. Open crowns. She hasn't won it all in New York since 2008, but her summer of 2012 would suggest that her drought there could come to an end next month.

Back to the men, the five-time major champion Djokovic broke through for his first-ever U.S. Open title last year after finishing as the runner-up there in 2007 (Federer) and 2010 (Nadal).

FYI: The French Open champion and reigning Aussie and U.S. Open runner-up Nadal will miss the U.S. Open for the first time since joining the ATP World Tour in 2003 due to tendinitis in his knees (he lost to Djokovic in last year's finale in Queens).

Djokovic was facing match point against Federer in their remarkable semifinal last year when the Serbian slugger saved his you-know-what with a mind- altering forehand cross-court return winner that landed in, much to the dismay of the Swiss great.

"Nole" would go on to post a come-from-behind win en route to his third U.S. Open final. He captured the Open to give himself three of the four major titles in 2011.

The Nadal-less 2012 men's field will not only feature Federer and Djokovic, but Olympic gold medalist and Wimbledon runner-up Andy Murray as well.

Murray still may not own a Grand Slam title, but his stunning straight-sets victory over Federer at the Games earlier this month whipped the British faithful into a frenzy, the type of tennis-induced frenzy not seen in Britain since Virginia Wade captured the women's Wimbledon title back in 1977.

The athletic Scot certainly figures into the U.S. Open equation. The 2008 runner-up to Federer just might have his big moment in Flushing in a couple of weeks. The Dunblane native clearly has enough game, and now seems to have the confidence to beat Federer or Djokovic under the brightest of lights.

Back over to the women.

Serena and Sharapova would appear to be the clear-cut faves, but they can probably expect challenges from several other ladies, most notably Azarenka, Radwanska, Petra Kvitova, Angelique Kerber, Stosur and a resurgent Li Na.

Azarenka has been No. 1 for most of the year since capturing her first major title in her first major final at the Aussie Open back in January. She opened her year with 26 straight wins before finally landing in the loss column with a setback against former Wimbledon runner-up Marion Bartoli at the big hardcourt event in Miami in March.

The Belarusian star has cooled off since the hot start, but she's definitely in the mix, as her current world No. 1 ranking would suggest.

Radwanska does not possess a big game, but always seems to be hanging around as the result of defense and timely shots. She's currently ranked second in the world after reaching her first career Grand Slam final last month, when she gave way to the mighty Serena at Wimby.

Kvitova and Kerber, ranked fifth and sixth, respectively, are the best left- handed women on the planet. The 2011 Wimbledon and WTA Championships winner Kvitova broke through with her first title of 2012 two weeks ago by winning it all on a hardcourt in Montreal, while Kerber simply continues to climb the charts, which will happen when you post eight wins against top-10 competition in one season.

The German Kerber, who was last weekend's Cincinnati runner-up to the former French Open champion Li, reached her first-ever major semifinal last year in New York, which wound up setting the stage for her tremendous 2012 campaign.

Stosur will be on hand as the defending champ, but her game has been just average since reaching a French Open semi a couple months ago. The super-fit Aussie stunned Serena in last year's U.S. Open finale for her first-ever major title.

Just don't expect a repeat performance this year.

As for Li, let's just say she hadn't been playing her best tennis since capturing the French Open last year.

But the veteran Chinese star has really picked up her game in recent weeks.

Li surprised in Montreal two weeks ago by making it to the final, where she lost to Kvitova, and rebounded beautifully from that setback by going all the way last week in Cincy. The 30-year-old veteran came from behind to best the sturdy Kerber in three sets in the finale at the Western & Southern event for her first title of 2012.

Back over to the fellas again.

Federer, Djokovic and Murray won't be the only studs in Flushing, where they can expect challenges from the likes of David "The Beast" Ferrer, former Aussie Open runner-up Jo-Willy Tsonga, former Wimbledon finalist Tomas Berdych and former U.S. Open champ Juan Martin del Potro.

Del Potro, who upset Djokovic in the bronze-medal match in London after losing to Federer in an epic 4-hour, 26-minute Olympic semifinal, is the only player not named Federer (2004-08), Djokovic (2011) or Nadal (2010) to win the U.S. Open title over the last eight years.

The tall Argentine is one of the hardest-working players on tour and would love to prove that 2009 was no fluke. "DelPo" came from behind to beat Federer in five sets in the Open final three years ago, which prevented the supreme Swiss from winning an unprecedented (in the Open Era) sixth straight U.S. Open championship.

Some other men to keep an eye on in Flushing are a pair of massive servers -- 6-foot-10 American John Isner and rising Canadian bruiser Milos Raonic. Isner has beaten both Federer (Davis Cup in Switzerland) and Djokovic (a semifinal at Indian Wells) this year, while the 21-year-old Raonic is a top-10 star in the making.

Is American Mardy Fish in the mix? Probably not. He's been getting his game together over the last couple of months after being sidelined for a few months with fatigue-like symptoms that ultimately led him to a minor (if that's possible) heart procedure.

Aside from Federer, Djokovic and del Potro, two other former men's champs also will be in the field -- former No. 1 players Andy Roddick (2003) and Lleyton Hewitt (2001) -- but neither one should figure into the equation this time around.

The women's field in Flushing will feature five former champions in Stosur, Serena, Sharapova, three-time winner Kim Clijsters and two-time champ Venus Williams, a former No. 1 who hasn't reached a U.S. Open final in 10 years, or since losing to her little sister in 2002.

The tennis career of Clijsters will officially come to end in New York. The Belgian wife and mother "retired" from the WTA in 2007 to start a family, only to return to the game in the summer of 2009.

Clijsters stunned the tennis world by capturing her second U.S. Open title in '09, then repeated the following year to give her a third straight title in Flushing. After winning the title in 2005, Clijsters missed the Open from 2006-08 because of injuries and/or "retirement" before returning for the big wins in '09 and '10.

The 29-year-old star missed last year's U.S. Open because of injury, which means she's seeking a fourth title there in her last four trips, as the outgoing Belgian star hasn't lost a U.S. Open match since 2003 when she fell at the hands of former top-ranked great Justine Henin in an all-Belgian final.

The former No. 1 Clijsters is quietly riding a 21-match winning streak on the hardcourts at the USTA Billie Jean King National Tennis Center.

Note: The all-time women's leaders in U.S. Open titles are Norwegian- born/naturalized American Molla Mallory, who piled up eight such championships from 1915-26, and the great Helen Wills (aka Helen Wills Moody), who tallied seven in a nine-year span from 1923-1931 in the Amateur Era.

The women's Open Era U.S. Open queens are Chris Evert (six), Steffi Graf (five) and Martina Navratilova (four).

Time for some picks.

Tough, tough call here for the men, but I'm going with Federer to make it Open title No. 6. For the women, you gotta go with another hot hand in Serena.

The 132nd men's edition and 126th women's edition of the U.S. Open will commence Monday in New York.