World No.1 Iga Swiatek is out of the Canadian Open after suffering a shock three-set loss to Brazil's Beatriz Haddad Maia.

The Brazilian beat the Polish star 6-4 3-6 7-5 to send shockwaves in the tournament in Toronto on Thursday.

Defending champion Camila Giorgi also bowed out, beaten by Jessica Pegula who joins Coco Gauff and Simona Halep in the quarter-finals.

In the opening set of their last-16 clash, Swiatek struck a double-fault to hand the unseeded Haddad Maia a 3-2 lead and the Brazilian leaned on her powerful serve and groundstrokes to close out the frame without facing a break point.

Swiatek fended off five break points to hold serve in a 15-minute opening game of the second set and later consolidated a break for a 5-2 lead before going on to force a decider.

World No.24 Haddad Maia broke Swiatek three times in the third set, including in the final game on her fourth match point when the Pole sent a forehand wide.

"I knew that all the matches here would be very tough, not only top 20 players, like the first round was a very, very tough round and I won in three sets as well," said the 26-year-old Haddad Maia during her on-court interview.

"Tennis is like that. It doesn't matter where you are playing, which court and with who. You need to push yourself to improve your game and I think that was the key for both (of my three-set) victories and I am very proud of myself."

Haddad Maia will play 12th-seeded Belinda Bencic in the last eight of the US Open tune-up event after the Swiss eliminated eighth-seed Garbine Muguruza 6-1 6-3.

American seventh seed Pegula rallied to beat Italy's Giorgi 3-6 6-0 7-5 and will next face either compatriot Alison Riske-Amritraj or Kazakh Yulia Putintseva.

Tenth seed Gauff beat sixth seed Aryna Sabalenka 7-5 4-6 7-6 (7-4) a day after ousting Wimbledon champion Elena Rybakina in a third-set tiebreak to set up a clash with 15th seed Halep, a 6-2 7-5 winner over Jil Teichmann.

"These type of matches, you know, the goal, yeah, to win the tournament. But I feel like for me I needed these matches leading up into the US Open," said Gauff. "So if I have a tough moment, I can look back on this."

With the win over Sabalenka, Gauff became the youngest player to reach back-to-back quarter-finals in Canada since Jennifer Capriati in 1990 and 1991.

Zheng Qinwen kept her breakthrough year on track, quieting the home crowd on Centre Court with a 7-5 5-7 6-2 win over Canada's Bianca Andreescu.

The Chinese 19-year-old, who reached the fourth round at Roland-Garros earlier this year, next faces Karolina Pliskova, who fired down 10 aces on the way to a 6-1 6-7 (11-9) 6-3 win over Greek powerhouse Maria Sakkari.