Roger Federer kept his bid for a fifth consecutive US Open title alive but was pushed to the limit by Igor Andreev as the world number two progressed to the quarter-finals with a gruelling 6-7 (5-7) 7-6 (7-5) 6-3 3-6 6-3 victory at Arthur Ashe Stadium.
Federer joins Novak Djokovic in the final eight after the Serb was made to work hard by Tommy Robredo for his quarter-final berth with an epic 4-6 6-2 6-3 5-7 6-3 victory.
However, fifth seed Nikolay Davydenko was not so fortunate as he crashed out after suffering a 6-4 4-6 6-3 7-6 (12-10) fourth-round defeat to qualifier Gilles Muller.
Federer was off the pace from the start, producing a number of poor shots before losing the first set in the tie-break when he sent a backhand wide to give Andreev set point before another wayward effort saw the Russian take the first set.
The second set once again went to tie-break. Federer raced into a 3-0 lead and although Andreev battled back to 3-6, the Swiss champion managed to level at one set all.
Federer, cheered on by the crowd, started to show the form he is capable of and comfortably won the third set 6-3 but Andreev continued to battle and took the encounter to a fifth when he produced a number of impressive serves to win the fourth set 6-3.
But Federer raised his game and came through a tough contest that lasted just over three-and-a-half hours when he claimed the fifth and final set after Andreev's attempted lob went long. He will now face qualifier Gilles Muller of Luxembourg in the last eight.
Djokovic also lost the first set of his match to the 15th-seeded Robredo before battling back to win the fourth-round meeting 4-6 6-2 6-3 5-7 6-3 in an epic contest that lasted three hours and 44 minutes.
The first set went with serve until the ninth game, when a double fault from the Australian Open champion handed Robredo his first break point of the match. The Spaniard did not pass up the opportunity, and went on to hold serve to go a set up.
After a strangely subdued opening, 21-year-old Djokovic burst into life at the start of the second set and soon built a 3-0 lead.
His momentum was halted when he had to call on the trainer to get treatment, seemingly for a hip problem, but was soon able to resume and - after each player held serve twice - capitalised on a double fault by Robredo to break again and level the match at one set all.
Sensing the Girona-born 26-year-old may be running out of steam, Djokovic broke Robredo in his second service game of the third set to establish a 3-1 advantage.
Robredo, making his fifth appearance in the fourth round, was looking to make the last eight at Flushing Meadows for the first time but could not find a way back with the remainder of the set going with serve.
Djokovic began brightly in the fourth set, breaking Robredo in the opening game, but the Spaniard refused to give up the fight and soon got back on level terms.
The Belgrade-born youngster was becoming frustrated at his opponent's never-say-die attitude and let his anger boil over in the seventh game, throwing his racquet down as Robredo edged 4-3 ahead.
Djokovic was then forced to serve to stay