Rafael Nadal held off a spirited challenge from world number 129 Nicolas Kiefer to earn a place in the US Open third round.
Third seed Nadal, still making his way back from an eight-week injury lay-off due to knee problems that left him unable to defend his Wimbledon title, had looked to be cruising to victory after taking the first set without the loss of a game.
He had not counted on the determination of his German opponent who made him fight for the remainder of the match before Nadal ran out a 6-0 3-6 6-3 6-4 winner at Arthur Ashe Stadium.
The victory means Nadal will next play fellow Spaniard and 32nd seed Nicolas Almagro, a five-set winner over American Robbie Ginepri and also completed a second round in which all of the top 16 seeds progressed to the last 32.
"I'm very happy to be in the next round," Nadal said. "I feel good, I started well, he started slow and later he played better.
"When you win the first set easy and like that and he starts to play better it's difficult. Nicolas is a great player, he played a good match and I'm very happy to beat him today."
Earlier in the day, second seed Andy Murray had bounced back from a lacklustre second set to reach the third round with a four-set win over Paul Capdeville of Chile.
Britain's world number two, playing in 80-degree heat at Arthur Ashe Stadium, beat his former training partner, ranked 87, 6-2 3-6 6-0 6-2 in two hours and seven minutes.
After taking the first set against world number 87 Capdeville, Murray, lost his way as the Chilean levelled the match.
The Scot, last year's runner up to Roger Federer, then got a second wind in the 80-degree heat, bouncing right back to take the third set to love before sealing a four-set win to book his place in the last 32 of the final grand slam of the year.
He will next play American wild card Taylor Dent, ranked 195 in the world, who beat Spain's Ivan Navarro in a fifth set tie-break.
"I played three very good sets and one poor one," Murray said. "But you're allowed to play a bad set sometimes.
"I came back well from it. I just felt a little bit lethargic, a little bit low on energy, I don't know why.
"But I managed to pick it up at the end when I needed to."
Sixth seed Juan Martin Del Potro stayed on course for a quarter-final meeting with Murray when he advanced with a three-set win over Jurgen Melzer, although his overall performance was inconsistent.
The Argentinian was pushed all the way in a first set lasting more than an hour before winning 8-6 on a tie-break.
Although he won the following two sets 6-3, last year's quarter-finalist produced four double faults and 36 unforced errors.
Jo-Wilfried Tsonga, seventh seed, also enjoyed a straight-sets win over Finland's Jarkko Nieminen.
While he had five double faults, the Frenchman won 92% of his points on his first serve and served 11 aces to win 7-5 6-3 6-4 and will next play compatriot Julien Benneteau, who eliminated 30th seed Victor Troicki of Romania, 6-1 3-6 6-1 6-0.
Ninth seed Gilles Simon had a straightforward 6-3 6-2 6-4 win over Thomaz Bellucci in just over two hours.
The Frenchman was rewarded for his greater consistency with his Brazilian opponent producing 44 unforced errors and three double faults.
Another Frenchman Gael Monfils, seeded 13th, also went through when he dispatched Germany's Andreas Beck 6-3 7-5 6-3 with Chilean Fernando Gonzales, the 11th seed, beating Josselin Ouanna of France 6-4 6-7 (5-7) 6-3 6-4.
Monfils next faces Jose Acasuso of Argentina after the world number 47 upset 18th seed David Ferrer of Spain 6-3 3-6 1-6 6-3 6-2.
Marin Cilic, seeded 16 and on course to face Murray or Dent in the fourth round, had to come from two sets down to overcome Jesse Levine 4-6 2-6 6-0 6-3 6-0 in a match lasting two and three quarter hours.
Tomas Berdych, seeded 17, beat Horacio Zeballos 6-3 6-7 (3-7) 7-6 (7-2) 6-2, Juan Carlos Ferrero - number 24 - came from two sets down to send Philipp Petzchner packing 1-6 3-6 6-4 6-2 6-4.
Serbian 30th seed Viktor Troicki was despatched by Julien Benneteau, the Frenchman winning 6-1 3-6 6-1 6-0 while Nicolas Almagro, seeded 32nd, edged out home favourite Robbie Ginepri 6-7 (7-9) 6-2 6-3 4-6 6-4.
Denis Istomin of Uzbekistan edged out Nicolas Lapentti 2-6 6-4 4-6 7-5 7-6 (7-4) while Daniel Koellerer beat Pablo Cuevas 3-6 6-2 6-1 6-4.