Agnieszka Radwanska wins 13th match in a row, into quarter final

Fourth seed Agnieszka Radwanska powered into the Australian Open quarter-finals on Sunday with a straight-sets win over former world number one Ana Ivanovic.

The Pole won her 13th match in a row in beating the Serbian 13th seed 6-2, 6-4 and will face Chinese sixth seed Li Na for a place in the semi-finals.

The pair had played each other seven times before with Radwanska winning their four previous meetings, most recently in Beijing in 2011, and she once again proved far too powerful and consistent.

"I'm very happy I could play my best tennis today," she said.

"Ana played more aggressively in the second set and was volleying well but in the important moments I was focused and glad I could close it out in two sets."

Ivanovic, who won the French Open in 2008 and was a Melbourne finalist in the same year, has lost weight and boosted her strength during the off-season as she looks to rediscover her best form.

But she got off to a bad start against Radwanska, getting broken on her first service game in blustery conditions.

Some neat cross-court winners showed glimpses of the Ivanovic of old but the in-form Radwanksa was making few errors and giving her opponent even fewer chances as she worked her way to a 3-1 lead.

After the Pole went 4-2 in front on a dubious line call that Ivanovic didn't challenge, she broke again in the next game and then took the set easily with an ace.

Radwanska, who is searching for her first Grand Slam title, maintained the pressure in the second set, breaking Ivanovic immediately, and there was no way back for the Serb.

She had chances to break in the fourth and sixth game but lacked the killer instinct in some entertaining rallies, with Radwanska wrapping up the match with an ace in 71 minutes.

Radwanska is the form women's player this year after winning warm-up tournaments in Auckland and Sydney. Her best Grand Slam so far was Wimbledon last year when she made the final and was beaten by Serena Williams.