OSAKA, Japan - Top seed and defending champion Sam Stosur cruised into the quarterfinals of the HP Open on Wednesday, blasting eight aces - including three in a row in one game - to beat Japan's Junri Namigata in straights, 60 63.

Stosur, who won her first singles title at this event last year, improved to 7-0 in her career at the event with the 63-minute victory over Namigata, who didn't even get on the board until the ninth game of the match (Stosur led 60 20).

"I also won the ITF title here in 2001, so I'm very confident when I play here," Stosur said. "My opponent hit the ball well. She has a good backhand, a pretty good first serve. I think she felt she needed to play well in front of her fans."

Stosur could face No.6 seed Kimiko Date Krumm next, if the 40-year-old Japanese icon wins her second round match on Thursday. "I'm looking forward to it! It will be my third Japanese opponent here, but the crowd has been supporting me a lot. It would be very tough for me if I play Kimiko."

It didn't take too long for the second seed, Marion Bartoli, to join Stosur in the quarters. Bartoli took just 69 minutes to roll past Stefanie Voegele, 62 62.

Later, No.4 seed Maria Kirilenko was forced to retire against Chang Kai-Chen due to a left hip injury after losing the first set, 6-4.

In the only match of the day pitting two unseeded players against each other, 33-year-old Tamarine Tanasugarn showed she still has what it takes to compete with the brightest young stars, rallying from 75 31 down to beat 18-year-old Coco Vandeweghe in three hours and two minutes, 57 75 64.