World No. 1 Novak Djokovic survived a three-set battle, while former world No. 1 Rafael Nadal and defending champion Roger Federer were quarterfinal losers Friday at the $2.43 million Western & Southern Open, an ATP Masters and U.S. Open Series event.

Djokovic battled back to beat sixth-seeded Frenchman Gael Monfils 3-6, 6-4, 6-3.

The victory moved Djokovic to an incredible 56-1 this year. The Serb is seeking his sixth Masters title of the season. Djokovic beat American Mardy Fish in last week's Masters finale in Montreal.

The Wimbledon and Aussie Open champion and 2010 U.S. Open runner-up Djokovic was the back-to-back Cincinnati runner-up in 2008 and 2009.

Djokovic will next do battle with eighth-seeded Tomas Berdych, who was a runner-up at Wimbledon last year. Berdych handled the third-seeded former No. 1 Federer 6-2, 7-6 (7-3) in an hour-and-a-half. The Czech masher has now won three of the last four meetings against the 16-time major champ.

The French Open runner-up Federer, who turned 30 last week, is a four-time Cincinnati titlist, including last year when he beat Fish in a quality final.

The seventh-seeded Fish took it to the second-seeded Nadal for a crowd- pleasing 6-3, 6-4 victory on the hardcourts at the Lindner Family Tennis Center. Fish prevailed in 1 hour, 39 minutes by smacking 12 aces, holding his big serve throughout, and breaking the mighty Spaniard on two occasions on Day 6. Fish ended the bout with an outstanding forehand cross-court winner.

Fish has yet to lose his serve this week.

The 29-year-old Fish recorded his first career victory against Nadal in seven tries and will now appear in his fourth straight semifinal. The American slugger captured the U.S. Open Series by winning on Friday and will now compete for the largest payout in tennis history at the U.S. Open -- $2.8 million, or $1.8 million for winning the U.S. Open and a $1 million bonus for winning the U.S. Open and U.S. Open Series.

The 10-time Grand Slam champion Nadal is the reigning U.S. Open and French Open titlist.

Fish was last year's Cincy runner-up to the great Federer.

The Minnesota native Fish's semifinal opponent on Saturday will be former Cincinnati champ Andy Murray. The American is 4-3 lifetime against the Brit, including a quarterfinal victory here a year ago.

Meanwhile, a fourth-seeded Murray peppered 10th-seeded Frenchman Gilles Simon 6-3, 6-3 on Friday. Murray is now a lopsided 7-1 lifetime against Simon, including seven straight wins.

The world No. 12 former top-10 star Simon was a champion in Hamburg last month.

The 2011 Australian Open runner-up Murray captured this Cincinnati tournament in 2008.

This week's winner will collect $496,000.