Coach Darren Cahill has paid tribute to Simona Halep's improved fighting spirit after the No.4 seed dug deep to end the Australian Open campaign of Belgian Elise Mertens.
The 16th-seeded Mertens had fought back hard on Monday to level the second set of their fourth-round encounter at 4-4.
It rekindled unhappy memories for Halep of last year's Qatar Open final, when Mertens had recovered from a set and a break down to beat the Romanian and claim the biggest title of her career.
But Halep ensured there would be no repeat at Melbourne Park, breaking the Belgian in a marathon ninth game and then serving out calmly for a 6-4 6-4 victory to set up a quarter-final clash with Estonian Anett Kontaveit.
"(Co-coach Arte Apostu-Efremov) and I spoke after that 4-all game in the second set after letting two breaks slip and then having chances in the 4-3 game," said Australian Cahill, who signed up late last year for a second stint as two-time major winner Halep's mentor.
"Then it got back to 4-all, she had break points in the 4-all game and missed them.
"One ball I think was a challenge on the side of the line.
"The old Simona would have let that game go, but she refused to give up in that game.
"That's what I'm most proud of, that fight that she's showing when a few things go against her.
"That's been the big change in her I have seen over the last two or three years."
Halep is the reigning Wimbledon champion, with her other major title coming at the 2018 French Open.
The Romanian star also lost the 2018 Australian Open final to recently-retired Caroline Wozniacki.
"I feel like I played a better match than all the matches since I'm here," Halep said of the victory over Mertens.
"I feel happy about that, and I'm trying just to stay focused.
"I like how I feel."
Kontaveit looked on the verge of victory when she led 5-1 in the final set against teenager Iga Swiatek.
The 18-year-old Pole got it back to 5-5, only for Kontaveit to steady and claim the 6-7 (4-7) 7-5 7-5 victory in a match lasting two hours and 42 minutes.
Kontaveit became the first Estonian to reach the last eight at an Australian Open.
But the free-swinging Swiatek still produced several of the match's most memorable moments, including a Nick Kyrgios-styled tweener shot in the 10th game of the second set.
Former French Open and Wimbledon champion Garbine Muguruza kept her quest for a first Australian Open title alive, the Spaniard outclassing Dutch ninth seeded Dutchwoman Kiki Bertens 6-3 6-3.
Unseeded at a major for the first time in six years, Muguruza will play Anastasia Pavlyuchenkova in the last eight after the Russian reached her third quarter-final in Melbourne with a 6-7 (5-7) 7-6 (7-4) 6-2 win over 2016 Open champion and former world No.1 Angelique Kerber.
Australian Associated Press