Madison Keys unlocks Elena Rybakina serve to reach Australian Open quarters

Melbourne: American Madison Keys upset sixth seed Elena Rybakina 6-3 1-6 6-3 in a roller-coaster match at Margaret Court Arena to march into the quarterfinals of the Australian Open on Monday and extend her win streak to nine matches this year.

Adelaide Open champion Keys had lost to the Kazakh in their last two encounters but was well in control for most of the last 16 tie, barring a rough patch in the second set when she lost four straight games.

Rybakina seemed to be struggling with a lower back injury that had affected her in the third round and Keys was able to play aggressively to neutralise her big serve and take control of the rallies.

"Her serve is such a weapon, so I knew that if I could just try to make at least some of her service games a little bit competitive, then I had a chance," said the 19th seed, who chalked up her third win over a top 10 player this month.

"So, I was basically just trying to make anything that I could get my racket on back over the net, which worked sometimes."

With her back against the wall, Rybakina was serving to stay in the first set when she made consecutive double faults to hand Keys the opener in 35 minutes.

Rybakina took a bathroom break before the start of the second and that took all the momentum away from Keys, who made more unforced errors in the first two games than she had in the opening set.

As Keys' level dropped Rybakina took full advantage and broke the American's serve three times to force a decider.

Keys had a crucial hold in the second game of the decider after it went to deuce five times and that seemed to give her the confidence to play her shots again.

The American moved up a gear and sealed her spot in the next round with a searing cross-court winner on her second match point.

"I've actually been working on trying to play a little bit more aggressive. I found that in the second set I got a little bit nervous, and I felt like I got a little bit passive," Keys said.

She will next play Ukraine's Elina Svitolina, who beat Veronika Kudermetova 6-4 6-1 earlier on Monday.

Rybakina said her back was in better condition going into the match, but the 25-year-old added that she was still in some pain and would take time off to rest before tournaments in the Middle East.

"The task for me now is to restore my back and work on the serve. Today, there were quite a lot of chances to hold it and I didn't come through," Rybakina said.

"In general, I need to work on moving to the net. There is still a lot that I need to work on."