London- World number one Simona Halep said it felt like a freight train hit her Monday after Serena Williams steamed past the top seeded Romanian and into the Australian Open quarter-finals.

Halep mounted a gutsy fightback after weathering an early onslaught but Williams kept her quest for a record-equalling 24th major alive with a 6-1, 4-6, 6-4 win.

“I felt like I had been hit by the train in the first set, everything was too fast,” Halep said.

It was Williams’ first match against a world number one since returning after having a baby in September 2017 and the American showed why many already regard her as the greatest of all time.

After rampaging through the early rounds without dropping a set, the 37-year-old was at least forced to work for her victory by Halep, who on paper is the top-ranked player in the world.

“It was an intense match and there were some incredible points,” Williams said.

“She’s the number one player in the world and there’s a reason why... (but) I’m such a fighter, I just never give up.”

Williams won her 23rd Grand Slam Down Under two years ago while two months pregnant and is the bookies’ favourite to claim an eighth Australian title, despite being seeded 16th.

Another major would match Margaret Court’s tally and Williams, who will meet Czech eighth seed Karolina Pliskova next, has been on a mission at Melbourne Park this year.

French Open champion Halep was in danger crumbling before she regrouped for a stirring comeback.

The pair brought out the best in each other’s game, with Halep chasing down balls like a terrier and Williams blasting down aces and winners.

However, Williams said she had more in the tank and should have won the match in straight sets.

“I can definitely go to a new level. I have to if I want to stay in the tournament,” she said.

There was a minor wobble when Williams allowed Halep to bring up three break points in the opening game, conceding with a double fault.

Australia Open Results

Women’s 4th round
Serena Williams bt Simona Halep
6-1, 4-6, 6-4
Naomi Osaka bt Anastasija Sevastova
4-6, 6-3, 6-4
Elina Svitolina bt Madison Keys
6-2, 1-6, 6-1
Karolina Pliskova bt Garbine Muguruza
6-3, 6-1
Men’s 4th round
Milos Raonic bt Alexander Zverev
6-1, 6-1, 7-6 (7/5)
Lucas Pouille bt Borna Coric
6-7 (4/7), 6-4, 7-5, 7-6 (7/2)
Kei Nishikori bt Pablo Carreno-Busta
6-7 (8/10), 4-6, 7-6 (7/4), 6-4, 7-6
(10/8)