Anett Kontaveit ousts seventh seed Jelena Ostapenko from Australian Open

Ostapenko looked inconsistent all through the match. (Reuters)

Estonia's Anett Kontaveit shrugged off a torrid second set meltdown to knock seventh seed Jelena Ostapenko out of the Australian Open on Friday.

The Estonian 32nd seed is into the last 16 at Melbourne Park for the first time after winning a rollercoaster match against the French Open champion 6-3, 1-6, 6-3.

"It was tough. she played so aggressive," said Kontaveit after winning in an hour and 53 minutes.

Kontaveit stormed through the first set, setting the tone by breaking Ostapenko in the very first game and repeating the dose three times to take a 5-2 lead.

It made the Latvian world number seven momentarily wake up, returning with power and precision to break back to love for 5-3.

Ostapenko saved two breaks points in the next but when a wayward forehand gave Kontaveit a third the number 32 seed took the opportunity to break for a fifth consecutive time and wrap up the set 6-3 after 36 minutes.

"I felt I started really well," said Kontaveit, who will play Spain`s Carla Suarez Navarro for a place in the quarter-finals. "I felt I played great in the first and third sets."

Ostapenko called the trainer before the start of the second set, complaining of trouble above her left knee and had her left thigh strapped during a medical timeout.

She emerged hobbling badly but it seemed to fire her up as a succession of heavy groundstrokes broke Kontaveit twice either side of holding serve for the first time to grab a 3-0 lead.

The huge momentum shift had an analgesic effect on Ostapenko's thigh.

She started bouncing around on her toes when returning serve, at one point scampering around her forehand to unleash a screaming winner down the line on her way to a 5-0 lead.

Nerves got to her when serving for the set but when she broke again to take it to 6-1 the tables were turned completely as Kontaveit this time went a whole set without holding serve.

The third set, unusually for this rollercoaster match, went with serve until Kontaveit made the decisive move in a seventh game that lasted almost 13 minutes.

The Estonian outlasted Ostapenko to convert her fifth break point after seven deuces to take a 4-3 lead which she soon made 5-3 with an easy hold before wrapping up the win.

"I just tried to stay with her in the third set until I got that break," said Kontaveit.