By Julian Linden

NEW YORK (Reuters) - The easy part is over for Roger Federer. The U.S. Open is about to get a lot harder for the Swiss master.

The 16-times grand slam champion is through to the quarter-finals and in majestic form, but most of his main rivals are too. Only Andy Murray has made an early exit.

Federer booked his place in the last eight with a 6-3 7-6 6-3 win over Jurgen Melzer at the Arthur Ashe Stadium on Monday without ever having to play at his best.

His next opponent is Robin Soderling, the big-hitting Swede who ended Federer's French Open defense earlier in the season.

If he gets through that, Federer could then face Serbia's Novak Djokovic, who beat him in the semi-finals at the Australian Open in 2008.

There is also Rafa Nadal, as always, lurking on the other side of the draw if they both reach the final. Federer may be the greatest player of all time but nothing is ever assured.

Soderling and Djokovic also moved through to the quarter-finals by winning on Monday.

Soderling overcame Albert Montanes, one of six Spaniards who made the last 16 of the men's draw, 4-6 6-3 6-2 6-3.

It was a workmanlike performance but Djokovic was all class and looks the more threatening. The world number three demolished the improving American Mardy Fish 6-3 6-4 6-1 and is steadily building momentum and confidence.


Sharapova was soundly beaten 6-3 6-4 but contributed to her own downfall with 36 unforced errors and nine double faults, including three in successive points. Her shrieks echoed around the center court.

She was one of two former U.S. Open champions from Russia that were beaten in straight sets. Svetlana Kuznetsova also departed, losing 7-5 7-6 to diminutive Slovakian Dominika Cibulkova, leaving Vera Zvonareva to fly the flag.

Federer is yet to drop a set in the tournament and hardly got out of second gear against Melzer.

He did have some problems with his serve and was broken once each in the first and third sets but was able to raise his game when it mattered.

Boris Becker, watching from the stands, nodded in approval. After the match, Federer shook hands with Alex Rodriguez and was invited to watch his New York Yankees play.

"I've never been to a baseball game so that's something on the 'to do' list for me," Federer said. "My schedule is busy so we'll see if I can make it or not."

Djokovic, getting better with each match after a shaky start to the tournament, provided a reminder of the form that saw him reach the final in 2007 then capture his maiden grand slam in Melbourne the following year with his best performance of the championship.


Next in line for Djokovic is Gael Monfils who overpowered his countryman Richard Gasquet 6-4 7-5 7-5 to become the first Frenchman in a decade to reach the U.S. Open quarter-finals.

"It's very encouraging at this stage of the tournament that I'm raising my game and feeling more comfortable on the court," Djokovic said. "I played a great match today."

Soderling has developed a reputation of a giantkiller after beating Nadal at the French Open last year the Federer this season. The odds are stacked against toppling Federer on the super-fast courts in New York but he holds no fears.

"I've played Roger many times. I know his game and he knows mine," Soderling said.

A surprise finalist 12 months ago but the top seed this year after the withdrawal of injured world number one Serena Williams, Wozniacki reminded everyone of just how far she has come.

"I definitely think I've improved a lot, not only physically, but also I believe in myself more. I believe I can do it," Wozniacki said.

Wozniacki's next opponent is Cibulkova, the only unseeded player left in the women's draw and also the smallest at just 1.61 meters (5-foot-3).

"Okay, I'm short, but, you know, I'm really quick," the 45th-ranked Cibulkova said. "I can be fast on the court and I have no problem with the low balls."

Estonia's Kaia Kanepi recovered from a horrendous start to wear down Belgium's Yanina Wickmayer 0-6 7-6 6-1 and reach the last eight against Zvonareva after the Wimbledon finalist outgunned Germany's Andrea Petkovic 6-1 6-2 in 67 minutes.

(Editing by Alastair Himmer)