Kerber magic act ends Hsieh fairytale

Former champion Angelique Kerber was forced to summon all the tricks in her locker to overcome Su-Wei Hsieh in an incredible fourth round victory at the Australian Open.

The commentators were frequently struggling for superlatives during one of the best matches of the tournament so far.

WHAT A CATCH!: Ballgirl delights crowd with classic grab

TRUE SPORTSMANSHIP: Kyrgios and Dimitrov share special post-match moment

Kerber, the 21st seed from Germany, looked down and out at one stage before completing a miraculous comeback in a 4-6 7-5 6-2 victory.

The win was Kerber's 13th of the year, including four at the Hopman Cup and five more while winning the Sydney International.

That title boosted her ranking back up inside the world top 20.

The 30-year-old said Hsieh, who hit 42 winners, played an "unbelievable match".

Doubles specialist Hsieh plays double-handed on both sides and confounded Kerber with some dinky drop shots amongst her repertoire.

"I was running everywhere and she always had the answer," Kerber said.

"She was playing a lot of corners and drop shots and I was just trying to run behind the ball and get them back."

Kerber's fitness was key to the victory and she believed it would hold her in good stead against Keys, who had an emphatic straight-sets win over French No.8 seed Caroline Garcia.

"It's another tough match but I am in the quarter-finals right now and just trying to continue how I played last week," Kerber said.

"I know she is a tough opponent but I am feeling good here."

Hsieh had already toppled plenty of big names before coming up against the 2016 champion and looked set to add Kerber to her list of high-profile scalps.

For long periods of the match the German had no answer to the Chinese Taipei player's brilliant but unorthodox style.

The World No.88 was one game away from winning the match at 5-4 up in the second set, with Kerber on serve.

But the German dug deep to hold, before finding another gear and breaking her opponent, then going on to level the contest at one set all.

From there on, all the momentum was with the two-time grand slam champion as Kerber raced away with the deciding set to set up a quarter-final clash with Madison Keys.

The American overpowered French eighth seed Caroline Garcia 6-3 6-2 earlier on Monday.

Keys, a semi-finalist at Melbourne Park in 2015 who made the US Open final last year, has yet to drop a set this tournament.

The 22-year-old missed the Australian Open last year after undergoing wrist surgery and said she was relishing being back.

"I am really excited and think I am playing well," Keys said. "Especially in tight moments, I'm handling my emotions well."

With AAP