MELBOURNE: Defending champion Victoria Azarenka survived a scare Saturday in a tough, three-set battle with injured American Jamie Hampton before booking her place in the Australian Open fourth round.

The top-seeded Belarusian came through the match on Rod Laver Arena 6-4, 4-6, 6-2 to set up a clash next with either 16th-seeded Italian Roberta Vinci or unseeded Russian Elena Vesnina.

But it was much tougher than the scoreline suggested against a player who was wincing in pain from a back problem that needed treatment in the second set.

The plucky Hampton had never played a Grand Slam third round before, and gave it her all in a match packed with quality rallies and tight games.

On a cool Melbourne day, Azarenka held her opening game with pinpoint serves and got a break in the fourth when Hampton hit a backhand into the net.

She turned the pressure up with some powerful groundstrokes from the baseline but Hampton refused to give up and had a break point in the fifth that she failed to convert.

Azarenka was being tested and was soon pumping her fist and shouting "C'mon" as her emotions showed, and her persistence paid off when a delicate lob handed her another break to be 5-1 in front.

But the 23-year-old Hampton bounced back, forcing Azarenka into a forehand error to keep the set alive.

The American held serve than broke again for 5-4 and Azarenka was in trouble before the Belarusian stepped up a gear and took the set on a Hampton double fault.

Hampton kept her focus and immediately broke for an early lead in the second set before throwing away her serve and it was back to level pegging.

Neither player was serving well and Azarenka got broken again, with her frustrations evident as she was pushed around the court.

Hampton was sizzling and had two set points at 5-3, but the top seed saved and held.

Hampton left the court for treatment on a lower back problem at the changeover, but despite being in obvious pain she held serve for the set, with Azarenka slamming her racquet in frustration.

The brave American, who appeared close to tears at times from the discomfort, had the crowd onside and got a crucial break in the third for a 2-1 lead before Azarenka fought back to win the next five games.

The victory keeps Azarenka on course to meet former world number one Caroline Wozniacki in the quarter-finals, and potentially Serena Williams in the semis, as she defends her first Grand Slam title. - AFP

Results from day six of the Australian Open on Saturday:

Women's singles

3rd rd

Maria Kirilenko (RUS x14) bt Yanina Wickmayer (BEL x20) 7-6 (7/4), 6-3 Svetlana Kuznetsova (RUS) bt Carla Suarez Navarro (ESP) 6-2, 4-6, 6-3 Victoria Azarenka (BLR x1) bt Jamie Hampton (USA) 6-4, 4-6, 6-2 - AFP

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