A off-season focus on fitness was behind Angelique Kerber's third-set resurgence as the former Australian Open champion clawed her way into the quarter-finals.
Kerber was on the ropes in her Rod Laver Arena clash on Monday against tricky Taiwanese veteran Hsieh Su-wei but regrouped for a 4-6 7-5 6-2 victory.
The German former world No.1 will take on in-form American Madison Keys in the final eight.
Hsieh, 32, rattled the world No.16 with her dinky drop shots and ability to find the lines playing double-handed off both sides as she fired 42 winners.
Hsieh was up 40-15 at 5-5 in the second set when Kerber showed her grit to level before slamming a forehand winner to break her opponent.
It proved a turning point as she went on to dominate the third against the doubles specialist.
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 after a lean 2017 following two grand slam titles the year previous.
Kerber said her summer success had come after some hard yards in training, with a switch to high-intensity sessions.
"I was really working hard on my fitness, because I knew this is a big part of my game," Kerber said.
"I think that was the key, at the end that I really could run forever."
Kerber said that as well as feeling fit she was in a good space mentally as she looked to repeat her feats of 2016.
"I'm feeling really confident and very good but let's see what a year will bring," she said.
"I just enjoy my tennis again, and I think this is the most important thing for me when I'm on court that I fight, that I play my game, and am enjoying it."
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