Serena Williams of the United States celebrates after defeating Romania's Simona Halep during their quarterfinal match at the Australian Open tennis championship in Melbourne, Australia, Feb 16, 2021. (HAMISH BLAIR / AP)

MELBOURNE - Serena Williams came through a huge test of her Australian Open title credentials to beat Simona Halep 6-3 6-3 in a high quality quarter-final and reach the last four at Melbourne Park for the ninth time on Tuesday.

Serena Williams went toe-to-toe with Simona Halep over 80 engrossing minutes on Rod Laver Arena before she was finally able to move to within two victories of a record-equalling 24th Grand Slam title

The 39-year-old American went toe-to-toe with the Romanian second seed over 80 engrossing minutes on Rod Laver Arena before she was finally able to move to within two victories of a record-equalling 24th Grand Slam title.

Williams, who mixed 24 winners with 33 unforced errors over the contest, has not won a major since her seventh Australian Open triumph in 2017 and next faces in-form Japanese third seed Naomi Osaka with a place in the final on the line.

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For Halep, who reached the semi-finals last year and was losing finalist in 2018, it was back to the drawing board as she looks to add to her two Grand Slam titles at the French Open and Wimbledon.

Japan's Naomi Osaka hits a forehand return to Hsieh Su-wei of Chinese Taipei during their quarterfinal match at the Australian Open tennis championship in Melbourne, Australia, Feb 16, 2021. (HAMISH BLAIR / AP)

Osaka thrashes Hsieh

In an earlier match, Osaka defeated Hsieh Su-wei with a clinical 6-2 6-2 win, two years after suffering a big scare in an emotional rollercoaster of a match against the Taiwanese maverick at the 2019 tournament.

On a warm and muggy day at Rod Laver Arena, Osaka attacked Hsieh’s weak serve with gusto and the Chinese Taipei giantkiller quickly wilted under the pressure of her Grand Slam quarter-final debut.

Osaka had a torrid time in her last Australian Open clash against Hsieh in 2019, needing to come back from a set and a break down on the way to claiming the championship.

Osaka said her dominance in the rematch on Tuesday showed how much better she had become at sticking to a plan rather than relying on her instincts.

“I would say for me today it was really important to have a plan just because she’s an opponent that I’m not really sure what’s going to happen,” Osaka said of the mercurial Hsieh, who beat her at Miami in 2019.

READ MORE: Osaka, Williams into Australian Open quarters; Thiem tumbles out

Hsieh, 35, bowed out after a stellar tournament, having become the oldest women’s player to debut in a Grand Slam quarter-final in the professional era.

Bulgaria's Grigor Dimitrov reacts during his quarterfinal match against Russia's Aslan Karatsev at the Australian Open tennis championship in Melbourne, Australia, Feb 16, 2021. (HAMISH BLAIR / AP)

Dimitrov: Back spasm to blame

Over at the men's side, a back spasm left Grigor Dimitrov unable to put his socks on, let alone pull them up, as the struggling Bulgarian exited the Australian Open quarter-finals with a 2-6 6-4 6-1 6-2 defeat to qualifier Aslan Karatsev.

The 18th seed, who had raced through the first four rounds in Melbourne without dropping a set, took a medical timeout after losing the third set but it did little to improve the situation.

“I just got a back spasm yesterday, and that was it,” Dimitrov said. “We couldn’t fix it on time. It happened early in the match and kept progressing. It was unstoppable.

Dimitrov, who earned the nicknamed “Baby Fed” as a junior due to similarities between his game and Roger Federer’s, is the latest player to be hit by injury in Melbourne with both Matteo Berrettini and Casper Ruud pulling out of matches on Monday.

Novak Djokovic and Rafael Nadal have also struggled with physical issues but remain in the tournament.

READ MORE: Nadal gathers strength as injuries strike rivals