Rafael Nadal looked far from invincible as the top seed survived a serious challenge from Sam Querrey on Monday to advance to the quarter-finals of the US Open.
Nadal took over three hours to dispose of the 20-year-old American 6-2 5-7 7-6 (7-2) 6-3 to move one step closer to another possible showdown with second seed Roger Federer.
"It was very difficult, especially after my big mistake in the second set," the Spaniard said. "I was playing normal, fine - nothing special, but nothing bad."
Nadal, who has won 42 of his last 43 matches and eight titles this year to take away the world's top ranking from Federer, appeared to be headed for an easy win after building a 4-2 lead with a break in the second set but Querrey broke twice to even the match.
Perhaps sensing the urgency, Nadal raised his game in the third-set tiebreaker, playing more aggressively and attacking the net. After winning the set, he pumped the air with his fist.
"The important thing is to win. When you are not playing your best, the important thing is to win," he said. "I did today, so I have a chance for practice tomorrow and to play another time on Wednesday. So that's the important thing."
Querrey, one of three Americans to advance to the fourth round, upset 14th seed Ivo Karlovic to make the round of 16 at the US Open for the first time.
Nadal, who is seeking his third Grand Slam of the year, will face Mardy Fish in the last eight after the American continued his surprising run at Flushing Meadows with a 7-5 6-2 6-2 rout of 32nd seed Gael Monfils.
Prior to this year, Fish had never advanced past the second round at the US Open and his only other quarter-final in a Grand Slam came last year at the Australian Open.
But the Florida native was playing well prior to the tournament, reaching the final in New Haven and beating Federer earlier this year at Indians Wells.
"I've always wanted to play well here," said Fish, who beat ninth seed and close friend James Blake in straight sets in the third round on Saturday. "I felt like I came here every time and lost in the second round. I'm glad to be moving on."
Fish, who will have Blake in his wedding party when he gets married on September 28, was pushed in a hard-fought opening set. Monfils broke to go up 4-3, but Fish broke back, then closed out the set on his third set point.
"I knew I had to be aggressive," Fish said. "He runs down a lot of balls. He moves extremely well. I tried to keep the points short."
Monfils seemed to lose focus, winning only two of the first 14 points in the second set as Fish jumped out to a 3-0 lead. After the third game, Monfils took an injury time-out to get his right knee taped.
Fish, however, was in complete control and closed out the match in just under two hours.
Sixth seed Andy Murray of Britain cruised through to the quarter-finals, beating Switzerland's Stanislas Wawrinka 6-1 6-3 6-3.
The 21-year-old easily disposed of Wawrinka in one hour and 49 minutes thanks to 38 winners and 37 unforced errors by the number 10 seed.
Murray took advantage of six of 13 break opportunities and held off