* Champion forced to dig deep against American
* Hampton first to take set off top six seeds (Writes through with quotes, adds byline)
By Ian Ransom
MELBOURNE, Jan 19 (Reuters) - Defending champion Victoria Azarenka survived a huge scare from an injury-hampered 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 with pain from a "messed up" back that forced her to leave the court for treatment but stunned the world number one with a barrage of forehand rockets to capture the second set and take a 2-1 lead in the third.
For a tormented Azarenka, it was a case of 'I'll have what she's having, please', as she waited in vain for the 23-year-old American to miss the lines on a sun-drenched Rod Laver Arena.
"She took a medical timeout but she rips winners all over the place. I was like 'can I have a back problem? I'm feeling great but I'm missing every shot!'" Azarenka said courtside after losing the match's winner count 41-17.
Hampton, a baseline pounder strong on both sides of the racket, has a history of back problems, and revealed she was suffering from two herniated (bulging) discs in her spinal column.
The affliction flared up at the French Open last year, leaving her unable to walk, and fears of a repeat at Melbourne Park were playing through her mind as she felt it start to pinch midway through the second set.
The pain made her try to shorten the points and go for broke against Azarenka. For nearly two sets the results were breathtaking.
"I was more focused on the cramping part of it because I have gone into a full-body cramp before. It's very painful. I was trying to manage that," the American told reporters glumly.
"I didn't go into the match thinking that I was going to lose. I went in with a lot of belief."
The injury took the most toll on her serve, however, and she began to wilt in the deciding set after Azarenka broke back to level at 2-2.
Smelling blood, the statuesque Belarusian started crunching her returns and pushing for the corners to make the American run. "I think she surprised everybody a little bit today," said Azarenka, bidding for a second grand slam title.
"I had to really just step up my game and try to, you know, get the most rhythm as possible and try to make her move, try to execute my shots, try to be more aggressive myself."
The counter-attack propelled Azarenka to a 5-2 lead and she closed out the match in two hours and nine minutes with a withering backhand return.
Playing in her first third-round appearance at a grand slam, Hampton became the first to take a set off the top six seeds at the tournament so far, following a series of one-sided routs.
Azarenka will next play Russia's Elena Vesnina or 16th seeded Italian Roberta Vinci. She said she felt she needed to improve "everything" about her game.
"These kind of matches sometimes... bring better things for you in the future, because winning ugly always means that you overcome something that you weren't feeling great, you weren't feeling all your shots," she added.
"So I take it as a positive in the end of the day." (Editing by John O'Brien)