Victoria Azarenka may be the only woman capable of stopping Serena Williams from winning her 17th Grand Slam singles title at the U.S. Open.
Or at least the only one capable of giving Williams a run for her money.
Azarenka, the No. 2 seed from Belarus, led Williams by a break in the third set of last year's Open final before ultimately losing, but she owns two victories this year over Williams on hardcourts.
So when Azarenka lost the first set to No. 13 Ana Ivanovic in Arthur Ashe Stadium on Tuesday, it appeared the women's draw might open up, allowing Williams a clear path to the championship.
But a shaky Azarenka rebounded for a 4-6, 6-3, 6-4 victory that propelled her into the quarterfinals, where she will meet unseeded Daniela Hantuchova. Because her match against Ivanovic was postponed from Monday because of rain, Azarenka must turn around and play the quarterfinals without a day's rest on Wednesday.
"I'm not concerned about the slow start, it's just a matter of getting that groove," Azarenka said.
Asked if she believed she can win the tournament, Azarenka added with a smile, "Yeah, if I didn't believe that then I wouldn't be here."
If she is going to win her first U.S. Open to go with her two Australian Open titles, she will have to do it while her boyfriend, the singer Red Foo, is in Australia.
"Why? Because he's a judge on the X Factor," Azarenka said. "I don't know why he's there. I'm not so happy about it either. I'm joking."
On the other half of the draw, Williams was slated to play Tuesday night in her quarterfinal against No. 18 Carla Suarez Navarro.
For the match, Azarenka broke Ivanovic nine times, and Ivanovic won less than 50 percent of her first-serve points.
Still, Azarenka looked unhappy and unsettled en route to losing a first set in which she made nine unforced errors against four winners. Meanwhile, Ivanovic in the first set resembled the player who won the French Open and ascended to the No. 1 player in the world in 2008. She smacked 17 winners, 11 off the forehand wing, against 10 unforced errors.
But in the second set, Ivanovic's well-known serve troubles reared their head, as she struggled with her toss and double-faulted five times en route to being broken four times.
"I think the biggest difference was the serve in the second set," Ivanovic said. "My percentage went right down."
"Her decline started almost from the moment she won that French Open in '08," TV commentator Pam Shriver said on air.
In the third set, Azarenka served for the match at 5-3, but was broken herself, one of seven breaks for Ivanovic. Ivanovic then served to tie it 5-all, but surrendered a 30-love lead, ultimately losing the match when she sent a backhand into the net.
But Azarenka survived and advanced to the quarters, and remains alive to potentially challenge Williams for the title.
"I think there's a lot of improvement I can do," she said.
Follow Adam Zagoria on Twitter @AdamZagoria for updates throughout the U.S. Open.