MELBOURNE (Reuters) - Defending champion Victoria Azarenka survived a huge scare from hard-hitting American Jamie Hampton, coming back from a break down in the deciding set to win 6-4 4-6 6-2 and reach the fourth round of the Australian Open on Saturday.

The 63rd-ranked American winced through the match with an apparent back injury, but went for broke against the Belarusian world number one, unleashing a barrage of forehand rockets to capture the second set and take a 2-1 lead in the third.

Azarenka dug deep to break the flagging Hampton twice and reeled off five successive games to win in two hours and nine minutes.

Azarenka will next play Russia's Elena Vesnina or 16th seeded Italian Roberta Vinci.

(Reporting by Ian Ransom; Editing by John O'Brien)