MELBOURNE, Australia - No.1 seed Simona Halep has made the Australian Open quarterfinals for the third time in her career, ending the run of unseeded Naomi Osaka, 6-3, 6-2 in one hour and 19 minutes.

"I played pretty good and I'm happy that I am back in the quarterfinals here," the WTA World No.1 said in her on-court interview. "I did not expect that at the start of the tournament because of my injury."

In the press conference, Halep said she couldn't quantify how her ankle had improved. "I'm not sure because I'm running a lot," she explained. "Maybe I get used to the pain and I'm not thinking that much that something can happen. Just taking every point. I'm trying to play 100%, which I was close today, to run normal and to run a lot."

The Japanese player, in the second week of a Slam for the first time in her career, had never beaten Halep - but in a pair of previous losses had taken the Romanian to three sets, impressively including in the third round of Roland Garros in 2016 in just Osaka's sixth pro match on red clay.

The first set once again illustrated the danger posed by the 20-year-old. Osaka's power was a known factor, which didn't prevent some of her sudden injections of pace - particularly on the backhand side - drawing gasps of breath. 

A crucial new dimension to her game, though, was her improved defence. Osaka has spoken over the past week of her off-season focus on her fitness, and the number of extended rallies in which she was able to keep up, and often outplay, Halep was evident.

But Halep who was showing no after-effects from her three-hour, 45-minute third-round marathon win over Lauren Davis, was at her sharpest at the biggest moments, fending off five break points in a crucial sixth game, frequently thanks to pinpoint serves down the tee that either went unreturned or set up easy putaways.

"I felt [the third-round win] a bit but not too much," acknowledged Halep. "This tournament is turning into a marathon for me, but happily I am still here."

Later, she discussed how she had recovered in the press conference: "First day after the match was pretty okay," explained the top seed. "Last night was really tough. I couldn't sleep. I had pain everywhere. But I slept before the match two hours, and worked perfect, perfect hours. I was, like, fresh after that. I felt good."

Naomi Osaka whips a backhand during her fourth round against Simona Halep (Getty)

Conversely, Osaka's forehand let the WTA World No.72 down in several key moments, missing putative winners by inches on her first break point opportunity at 2-1, again on break point in the sixth game - and once more when, having lost that tussle, she faced a break point of her own to fall behind 3-4. Early in the second set, too, 30-30 points on the Osaka serve - and subsequently both games - were lost to marginally errant forehands.

Having toughed out the mental test of the opening set, in which she had to survive deuce in each of her service games, Halep upped the pressure in the second. Maintaining the height and depth of her groundstrokes with metronomic consistency, the 26-year-old also responded to Osaka's pace by using it to create reflex winners of her own, such as the backhand down the line with which she held for 2-1 - having saved another two break points.

"About the game, I moved her," said Halep afterwards. "I tried also to push her back... She couldn't dominate the game. I did, I dominated. I went to the net a lot. I finished the point when I felt that it's time."

Seizing her chances to put points away at net with more relish than usual, Halep successfully smothered her opponent's game as it became increasingly error-strewn: though both would strike 22 winners today, Osaka's 31 unforced errors proved costly compared to Halep's mere 18.

The two-time Roland Garros runner-up wasted no time in closing out the match, hammering a forehand return winner crosscourt on her first match point to break Osaka for the third time in the set to seal a quarterfinal place in Melbourne for the first time since 2015. There, in her bid to progress to the last four for the first time, Halep will meet either No.6 seed Karolina Pliskova or No.20 seed Barbora Strycova.