Williams, after winning the Australian Open, didn't practice until Monday, and was relieved to get through the first round of the indoor tournament she's won twice. Her second-round match was easier, as Williams took less than an hour to beat the Croatian qualifier, converting her first match point with a forehand return winner down the line.
Next up will be French qualifier Emilie Loit, whom Williams hasn't met in six years.
"She's a lefty, she uses a lot of spins and slices,'' Williams said about Loit. "She's a very experienced player and tricky.''
Also joining Williams in the last eight were second-seeded Jelena Jankovic, third-seeded Elena Dementieva, fifth-seeded Alize Cornet, and Amelie Mauresmo, who has the most wins in the tournament's history.
Jankovic, who lost her No. 1 ranking when she lost in the Australian Open fourth round, overcame Li Na of China 6-0, 3-6, 6-2 for the first time in five hard-court matches.
"There are certain players who give you a hard time no matter what their ranking is,'' Jankovic said of 28th-ranked Li. "It's just their game and their style of play that doesn't kind of suit mine. But today I came out with a good tactic.
"I kept hitting the ball very deep and very hard and I took the initiative.''
Dementieva won her first meeting with Russian compatriot, 17-year-old Anastasia Pavlyuchenkova, 6-4, 6-2, taking seven consecutive games in the middle en route to her sixth quarterfinal appearance at the Open GDF Suez.
There she'll meet French wild card Nathalie Dechy, who upset sixth-seeded Patty Schnyder 3-6, 6-4, 6-3. Dechy made it to the quarters for the first time since 2000.
Cornet rallied past Daniela Hantuchova 1-6, 6-4, 6-2, beating the Slovakian for the second time in less than a month. Cornet also won from a set down in the Australian Open third round.
"I've had the experience from my previous matches against her,'' Cornet said. "She got off to a very good start again. But in the second set, her form always drops. I was on the lookout for an opening to rush into it and put her under pressure.''
Cornet will meet Jankovic next.
Eighth-seeded Mauresmo routed Monica Niculescu of Romania 6-1, 6-2, improving her tournament-best win-loss record to 27-10. Mauresmo has reached the final five times, won twice, and was runner-up in both of Williams' victories. The French star was on the opposite side of the draw again from Williams, and faces fourth-seeded Agnieszka Radwanska in the quarters.
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