The 19-year-old from Poland thumped 30 winners and outplayed Halep in all areas of the court to win 6-1 6-2 on Sunday.

Halep and Swiatek met at the same stage last summer with the Pole, a former junior Wimbledon champion, managing to win just one game.

The teenager appeared stunned after this famous victory, saying: "I don't know what happened. I felt like I was playing perfectly. I was so focused the whole match. Even I am surprised that I can do that."

The loss ended Halep's career-best winning streak of 17 consecutive matches, guaranteeing that Barty - who chose to skip the US and French Opens due to concerns about coronavirus and her preparation - would finish the year atop the world rankings.

But the Romanian was able to keep the loss in perspective.

"I realise that it was a fantastic year with all the tough moments that we all had, so I'm not going to ruin the whole year just for a match," Halep said.

"Of course it's not easy to take it, but I'm used to some tough moments in this career.

"So I will have a chocolate and I will be better tomorrow."

It was immediately clear on Sunday how much Swiatek has developed in the last year as she raced into a 3-0 lead.

She hit 17 winners in the first set and, although Halep made only two unforced errors, she was simply not able to get into the match.

The Romanian began to shoot panicked glances towards coach Darren Cahill as Swiatek moved ahead again early in the second set, the teenager showing no signs at all of stage fright.

Halep tried to fight back but more often than not it was Swiatek winning the biggest points and she was nerveless in serving it out.

It was a disappointing ending for world No.2 Halep, who had not lost a match since the Australian Open.

Another major shock swiftly followed as Italian qualifier Martina Trevisan defeated fifth seed Kiki Bertens 6-4 6-4 to set up a clash with Swiatek.

"I came here two weeks ago to play the qualifiers and today I'm here in the quarter-finals. I can't believe it," said Trevisan, who will break into the top 100 of the WTA rankings on Monday.

Halep's exit means there is guaranteed to be a new French Open champion, with third seed Elina Svitolina now the highest-ranked player left and the only seed in the top half.

Sofia Kenin and Petra Kvitova, who are both in the bottom half, are the only slam champions remaining.

Svitolina will know what a huge chance this is for her to make a first slam final and she was impressive in a 6-1 6-3 victory over French favourite Caroline Garcia.

Meanwhile Czech left-hander Petra Kvitova reached the quarter-finals here for the first time in eight years as she overpowered China's Zhang Shuai 6-2 6-4.

Seventh seed Kvitova's superior firepower proved decisive as she posted her fourth successive straight-sets victory.

Kvitova will now meet unseeded German Laura Siegemund, who came through a tight opening set before cruising past Spaniard Paula Badosa 7-5 6-2 to reach her maiden grand slam quarter-final.

Both players struggled on serve in the opening set of their see-sawing fourth-round meeting on Court Simonne Mathieu, before Siegemund switched gears at 5-5 to claim the decisive break and take the early advantage in the contest.

Badosa, a former junior champion who knocked out 2017 winner Jelena Ostapenko in the previous round and 2018 runner-up Sloane Stephens in her second match, found herself down 3-1 in the second set as Siegemund turned up the heat.

World No.66 Siegemund fought off a spirited comeback attempt from Badosa to stretch the lead further with a break in the seventh game of the second set, before closing out her victory in style.

Australian Associated Press