Serena Williams took another step in her comeback from a chronic left knee injury, beating Bethanie Mattek 6-3, 6-1 to advance to the quarterfinals in the Western & Southern Financial Group Women's Open on Thursday.
Williams, playing in her first tournament since the Australian Open in January, will face Amy Frazier in the quarterfinals on Friday.
"I'm just taking it one match at a time," Williams said. "I didn't expect super-spectacular results, but I didn't expect bad results, either. I'm not looking too far ahead - one match, one match, one match."
Williams committed 14 unforced errors to seven by fellow American Mattek in the 37-minute first set, but had five aces to Mattek's none.
The seven-time Grand Slam singles champion lost the first game of the second set to the 105th-ranked Mattek before taking the next six games. Williams won the last 10 points of the match, breaking Mattek at love in the final game.
"She just started hitting winners," Mattek said. "She turned it up a little bit. I started missing shots a little bit and having a little trouble getting my serve in, and she took advantage of it."
Williams said she didn't play as well as she had in her first-round win over second-seeded Anastasia Myskina, but still felt she was improving.
"I feel fine," Williams said. "I'm doing a lot of work off the court, and I hope it pays off, because I hate it. I feel like I can be faster, not just faster, but quicker."
Fifth-seeded Jelena Jankovic outlasted Maria Elena Camerin of Italy 6-4, 6-4 in a second-round match featuring 12 breaks of serve. The second set was interrupted by a rain delay which lasted almost 30 minutes.
"My legs started hurting a little bit," Jankovic said. "I was glad I was able to finish it in two sets. At the end, I was saying to myself, 'I don't need any unforced errors.' I didn't want to play three sets. I was starting to get tired."
The Serb faces former top-10 player Vera Zvonareva of Russia in the quarterfinals. They're 1-1 from previous matchups. Zvonareva routed Varvara Lepchenko of Uzbekistan 6-0, 6-2 with six breaks.
It's Zvonareva's first quarterfinals since she won her fourth career title in the Wimbledon warmup at Birmingham last month.
Sixth-seeded Marion Bartoli of France beat qualifier Vasilisa Bardina of Russia 6-2, 2-6, 6-3. Bartoli will face fourth-seeded Katarina Srebotnik on Friday.