Flushing Meadows, NY -- (Sports Network) - It took more than 3 1/2 hours, but Roger Federer kept alive his quest for a fifth straight U.S. Open title, earning a fourth-round, five-set victory over 23rd seed Igor Andreev of Russia.

Federer's 6-7 (5-7), 7-6 (7-5), 6-3, 3-6, 6-3 victory advanced him to the quarterfinals against an unlikely opponent, Gilles Muller of Luxembourg. Muller upset fifth-seeded Russian Nikolay Davydenko, 6-4, 4-6, 6-3, 7-6 (12-10).

The second-seeded Federer ran his winning streak to 31 at the U.S. Open, last losing in Flushing in 2003. The former long-time world No. 1 Swiss, a 12-time major champion, overcame 60 unforced errors, but dominated at the net, winning 58 of a possible 84 points. Conversely, Andreev was just 12-of-28 on his net approaches. Also, the Russian converted just 2-of-15 break point chances.

Federer won the first three games of the final set, which included a key break of serve in the second game. Andreev was successful on a drop shot, but Federer returned the ball to the right corner, and the Russian's backhand went wide as the Super Swiss went up 2-0.

Then came four break point saves by Federer in the seventh game, when he went ahead 5-2 before finally serving out for the match.

It marked just the third time ever that Federer has played five sets at the U.S. Open.

"I'm very happy with the score, of course you always wish three sets," said Federer. "Honestly, those five-setters are pretty fun too."

Davydenko reached the semifinals here the last two years, but couldn't handle Muller's expert play at the net. Muller converted 35-of-47 net approach opportunities.

Last year's runner-up Novak Djokovic was a hard-fought fourth-round winner Tuesday. The third-seeded Djokovic came from behind to beat game 15th-seeded Spaniard Tommy Robredo 4-6, 6-2, 6-3, 5-7, 6-3 on Day 9 at the USTA Billie Jean King National Tennis Center.

Djokovic struggled mightily physically on a warm Tuesday at the year's fourth and final major. The Serb was bothered by an upset stomach and a sore ankle, but ultimately outlasted the pesky Robredo in 3 hours, 44 minutes.

The 21-year-old Djokovic broke Robredo to grab a 3-2 lead in the fifth and final set and broke again four games later to finally end the battle at Ashe Stadium.

Djokovic converted on his first match point when Robredo netted one final forehand. The Serb, who let the Spaniard hang around by committing 58 unforced errors, wound up with 11 aces and broke Robredo's serve six times.

The 6-foot-3 Djokovic was last year's U.S. Open runner-up to Federer and captured the Australian Open title back in January.

The Olympic bronze medalist Djokovic will meet Tuesday night's Andy Roddick- Fernando Gonzalez winner in the quarterfinals. Roddick is a former world No. 1 who titled here back in 2003.