Serena Williams beats Victoria Azarenka at U.S. Open

Reporting from New York — Serena Williams dropped into the splits Saturday on Arthur Ashe Stadium as she made an unexpected stop, imagining she could somehow hit a winner while appearing as if she were a gymnast who had just completed a tumbling pass.

Williams needed something spectacular because she was pushed hard by fourth-seeded Victoria Azarenka in the third round of the U.S. Open.

The 29-year-old Williams won 6-1, 7-6 (5) in a match that took nearly two hours and featured shot-making more appropriate for a final than one on the first weekend of the season’s final major.

In the fourth round Williams, seeded 28th, will play 16th-seeded Ana Ivanovic who ended the fun run of 18-year-old Sloane Stephens of Los Angeles with a 6-3, 6-4 win.

“I think in the first set I played some really good tennis,” Williams said. “In the second set she played really, really good tennis.”

Azarenka, a clever and hard-hitting 22-year-old from Belarus, was overwhelmed by Williams at first. She lost the first five games in 17 minutes and the first set in 28 minutes.

“What is that like?” Azarenka asked”It’s painful. To have somebody just going at you, it’s a little bit painful. You try to do your best, but somebody’s on fire.”

Williams blasted six aces, including four in a row over two games, and the match was compelling only in the despair Azarenka seemed to be feeling as she missed shot after shot, unable to force Williams into any place on the court where it wasn’t comfortable for the 13-time major champion to pound a winner.

“Yeah, 17 minutes was kind of fast to go down 5-love,” Azarenka said. “She started really strong and didn’t give me much space to just be out there.”

Azarenka makes moaning sounds every time her racket makes contact with the ball, and sometimes the fans mimicked her escalating noises, but they also began to cheer for her when she started to find her game in the second set.

Still, the end seemed inevitable when Williams got the first service break in the seventh game of that set with a ferocious cross-court passing shot and then held serve for a 5-3 lead.

In fact, in the ninth game Williams and Azarenka started walking off the court after Williams forehand flew past Azarenka on the sideline on a match point. But the ball was called out and the video review requested by Williams showed that her shot was wide.

Given another chance, Azarenka shed her hesitancy and became aggressive. She began smacking forehand winners everywhere. When Williams tried to serve out the match, Azarenka pushed back again, forming rallies that often ended with Williams out of breath and out of position.

Finally, on her fifth match point, in the tiebreaker, Williams made a hard return of an Azarenka serve and when Azarenka’s reply was a wide forehand, Williams screamed with both joy and relief.

In other notable matches, third-seeded Roger Federer dropped a set for the first time but won his third-round match over 27th-seeded Marin Cilic, 6-3, 4-6, 6-4, 6-2. Eighth-seeded Mardy Fish still hasn’t lost one, though. He beat South African Kevin Anderson 6-4, 7-6 (4), 7-6 (3). … So far 14 men and women have retired from singles matches because of injury or illness. That’s already a Grand Slam tournament open-era record.

diane.pucin@latimes.com

Twitter.com/mepucin