NEW YORK – Novak Djokovic and Andy Murray have met in three of the last four Grand Slam finals, though if they play in the U.S. Open this year, it will be in the semis.

Each took a step forward Friday, shaky at moments and sensational in others, in second-round victories.

The top-seeded Djokovic faced two early set points, while defending champion Murray had to go four sets.

After pulling out the first set in a tiebreaker, Djokovic needed less than an hour to close out his victory.

The 2011 champion beat 87th-ranked Benjamin Becker of Germany 7-6 (2), 6-2, 6-2.

Becker had a chance to serve for the first set at 5-4. But he wasted the first with a forehand into the net and the second when a backhand sailed wide.

"Becker is a quality opponent and he should have won the first set," Djokovic said. "I was fortunate enough to come back and win the first set, and after that, I was much more comfortable on the court."

Leonardo Mayer, ranked 81st, ran Murray all over the court, but the third-seeded Brit excels at chasing down shots.

Murray won the last five games for a 7-5, 6-1, 3-6, 6-1 victory.

"He's a big hitter of the ball. I had to defend a lot," Murray said. "I think he played some really, really good tennis. It made for an entertaining match."

The wind was swirling at Arthur Ashe Stadium, as it often does during the day, to players' frustration.

Another Grand Slam winner, Li Na, also showed some championship form earlier on Ashe.

This time, her opponent, Laura Robson, looked very much like a teenager.

The fifth-seeded Li avenged her third-round upset loss to the young Brit at last year's U.S. Open, winning in straight sets at the same stage at Flushing Meadows.

Li, the 2011 French Open champ, rallied from down a break in the second set for a 6-2, 7-5 victory.

Australian Open semifinalist Sloane Stephens, seeded 15th, beat fellow American Jamie Hampton 6-1, 6-3. Hampton, at No. 23, was seeded at a Grand Slam tournament for the first time in her career.

Third-seeded Agnieszka Radwanska and No. 9-seeded Jelena Jankovic each pulled out tough straight-set victories.

Wimbledon runner-up Sabine Lisicki, seeded 16th, was eliminated in straight sets by Ekaterina Makarova. The 24th-seeded Russian won 6-4, 7-5.

Fifth-seeded Tomas Berdych beat Denis Kudla of the U.S. 7-6 (3), 7-6 (3), 6-3.

American Tim Smyczek, ranked 109th, reached the third round at a Grand Slam tournament for the first time. He edged 73rd-ranked Alex Bogomolov Jr. in five sets, needing nearly four hours to win 3-6, 7-6 (6), 2-6, 6-4, 6-4.

Two other U.S. Open winners, Juan Martin del Potro and Lleyton Hewitt, were to face each other Friday night.