Days after Venus Williams pulled out of the U.S. Open citing health reasons, sister Serena entered the fourth round of the tournament to become the lone American left in the race.

The 29-year-old three-time champion defeated fourth seeded Victoria Azarenka 6-1, 7-6 (7-5) to retain hopes a U.S. podium finish in the women's draw and keeping alive the legacy of iconic sisters who ruled women's tennis most part of the last decade.

In her next round Serena will face the 16th-seeded Ana Ivanovic who defeated American teenager Sloane Stephens of Los Angeles 6-3, 6-4. Williams is seeded 28th in the tournament.

The high-quality match replete with splendid shot making lasted nearly two hours and Serene mustered her experience to pull off a win.
Although Williams won the first set with pretty little effort, the second lasted like eternity and she was not impressed with her performance.

I think in the first set I played some really good tennis ... In the second set she played really, really good tennis, she said.
She served for as many as five match points in the 82-minute set before clinching the win that makes her the only American player to reach the fourth round this year, after a slew of teenagers lost out on the way.

I definitely wasn't happy with the way I played overall today ... You know, I was a wee bit disappointed. But I can build on it, she said in the post-match news conference.

Williams had entered the tournament as the betting favorite, the San Francisco Chronicle reported. She was the favorite with 9-to-5 odds of winning her fourth title, the report said, citing Las Vegas Sports Consultants.

Earlier, her sister Venus pulled out of the tournament due to Sjögren's Syndrome, an autoimmune disease she had recently been diagnosed with.

The two-time champion at Flushing Meadows was set to contest Germany's Sabine Lisicki when she made the startling revelation.

I'm really disappointed to have to withdraw from this year's U.S. Open, said the former world number one in a statement. I enjoyed playing my first match here and wish I could continue but right now I am unable to. I am thankful I finally have a diagnosis and am now focused on getting better and returning to the court soon.