World No. 1 Serena Williams eased into the next round in straight sets while stomach problems sent Wimbledon champion Marion Bartoli crashing out of the WTA Rogers Cup in Toronto on Thursday.
Two-time champ Williams avenged an earlier loss by her sister, Venus, to Kirsten Flipkens by routing the Belgian 6-0, 6-3 in a third round match in the $2.4 million tournament at the Rexall Centre stadium.
Flipkens, a surprise semi-finalist at Wimbledon, ousted Venus Williams 0-6, 6-4, 6-2 in the first round.
Williams, the reigning US Open and French Open champion, won this tournament in 2001 and 2011 and was the runner-up in 2000.
The American blasted 10 aces, had just one double fault and lost just one point on her second serve in the 56-minute match.
Williams moves on to the quarter-finals where she faces Slovak Magdalena Rybarikova.
French seventh seed Bartoli was upset by Rybarikova 7-6 (7/5), 1-0. Bartoli retired with abdominal pain after losing the first game of the second set.
Last week Rybarikova captured her second consecutive Washington, D.C. crown.
Third-seeded Agnieszka Radwanska dispatched 14th-seeded American Sloane Stephens 6-1, 7-6 (7-2) and fourth-seeded Chinese star Li Na rallied to beat former world No. 1 Ana Ivanovic 3-6, 6-1, 7-6 (7/5).
Former French Open champion Li battled back from 5-2 down in the third set to beat Ivanovic.
Ivanovic stormed to a 6-3, 1-0 lead Thursday but then Li won six straight games to take the second set.
Ivanovic jumped ahead 5-2 in the third before Li charged back, winning four of five games to force a tiebreaker which she won.
"At the start of the second set I began hitting the ball into the court more," said Li.
"If I played a little bit soft, she was attacking a lot."
Li said it became a battle of attrition so she just kept being aggressive.
"I was just trying to see if I could turn it around, and I'm happy I was able to. Sometimes you can't play your best, but you just hang in there until the end," said Li, who lost to Czech left-hander Petra Kvitova in last year's Rogers Cup final.
Fifth-seeded Italian Sara Errani outlasted France's Alize Cornet 7-5, 7-6 (7/3). Errani will meet 2012 Wimbledon runner-up Radwanska in the last eight.
Romanian Sorana Cirstea surprised 15th-seeded Serb Jelena Jankovic 6-3, 6-4.