Despite being the 16^th seed, Williams is viewed by many as the favourite to claim the singles title at the first Grand Slam of the year.

She had enjoyed comfortable straight sets wins in her first three matches but was expected to face a greater challenge with world number one Halep showing signs of her best form.

However, the first set proved a comfortable one for Williams as the American pressured Halep’s serve and clinched the opener 6-1.

Romania’s Halep responded impressively to the early setback and the French Open champion broke in the final game of the second set to force a decider.

The match continued to live up to expectations, with Halep forcing three break points on the William’s serve only for the American to hold.

It proved a critical moment as Williams broke in the following game before sealing a 6-1, 4-6, 6-4 victory.

The result keeps Williams’ hopes of an eighth Australian Open title on track and also maintains her pursuit of matching Margaret Court's all-time record of 24 Grand Slam crowns.

Karolína Plíšková will face Williams in the next round after the Czech player dispatched Spain’s Garbiñe Muguruza 6-3, 6-1.

Japan’s Naomi Osaka, who beat Williams in the 2018 US Open final, remains on course for a potential rematch with the American in the semi-finals.

Osaka came from a set down for the second successive match to advance as she beat Latvia’s Anastasija Sevastova.

Her next opponent will be Elina Svitolina of Ukraine as the sixth seed beat American Madison Keys 6-2, 1-6, 6-1.

In the men's draw, world number one Novak Djokovic reached the Australian Open quarter-finals for the 10^th time in his career.

The Serbian, a six-time champion, overcame Russia’s Daniil Medvedev 6-4, 6-7, 6-2, 6-3 after a challenging match.

Japan’s Kei Nishikori came through an equally testing tie to set up a last eight clash with Djokovic.

Nishikori battled from two sets down to clinch a 6-7, 4-6, 7-6, 6-4, 7-6 win over Spain's Pablo Carreño Busta.

Fourth seed Alexander Zverev had been billed as the likeliest of the next generation of top men’s players to earn their maiden Grand Slam title in Melbourne.

The German’s challenge fell short in the fourth round, however, as he was beaten 6-1, 6-1, 7-6 by Canada’s Milos Raonic.

Zverev showed his frustration in the second set by destroying one of his rackets.

The result saw Raonic advance to a quarter-final match with France’s Lucas Pouille, who beat Croatia’s Borna Coric 6-7, 6-4, 7-5, 7-6.