Simona Halep had to be at her counter-punching best to see off a determined second-set comeback from Elise Mertens on Monday as the Romanian world number three advanced to the quarter-finals of the Australian Open with a 6-4 6-4 victory.
Halep, a beaten finalist at Melbourne Park two years ago, will next meet either Estonia's 28th-seed Anett Kontaveit or Poland's Iga Swiatek in the last eight.
Mertens, who beat Halep in the Doha final last year, blasted bags of winners but also made 38 unforced errors as Halep chased down every ball and made the Belgian work for every point.
Mertens stormed back from a double break 3-0 deficit in the second set to level at 4-4, only for Halep to break in a marathon ninth game and serve out to advance to the last eight.
"Against her in Doha in the final I was leading a set and 4-2 and lost the match so I knew I had to stay focused until the end," two-time Grand Slam champion Halep said.
"To be honest I got a bit nervous at 4-3 (in the second).
"I had to calm down because when I get nervous I get a bit crazy on court so I had to stay cool and get energy from the box and not think (about the past). "But I was strong enough to finish the match."
The pair broke each other once in the first eight games as they engaged in lengthy rallies of high quality shot-making.
The Romanian, however, managed to crack Mertens in the crucial ninth game when she jumped on a double fault at 15-30 and then sealed her second break with a forehand winner that allowed her to serve out in the 10th game.
Halep broke in the first game of the second set and while Mertens put her under all sorts of pressure in the next game, the fourth seed managed to scramble and keep the rallies alive.
But the Belgian finally got some traction when she got a break back and then held serve to get back to 3-2, conceding just one point in the two games.
She broke again in the eighth game as a frustrated Halep remonstrated with her box and whacked her racquet into the ground without breaking it.
That outburst seemed to help as she put Mertens under intense pressure in the 11-minute ninth game, which she took on her fifth break point opportunity, then sealed the win on her next service game.