Number one Swiatek upset by Haddad Maia in Canadian Open last-16 clash
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 number 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," Haddad Maia said 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."
French Open champion Swiatek, who had a run of 37 straight wins halted in the third round at Wimbledon last month, said she struggled with the windy conditions.
"Next time maybe I'm going to be able to find, even though the conditions are going to be bad, more solutions and just play more solid. Because I did a lot of mistakes that I kind of don't accept," she told reporters.
Haddad Maia will play Belinda Bencic (25) of Switzerland in the last eight of the US Open tune-up event.
A day after ousting Wimbledon champion Elena Rybakina (23), 10th seed Gauff beat sixth seed Aryna Sabalenka (24) 7-5 4-6 7-6(4). The American will next face 15th seed Halep (30), who beat Jil Teichmann (25) 6-2 7-5.
"These type of matches, 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 becomes the youngest player to reach back-to-back quarter-finals in Canada since Jennifer Capriati in 1990 and 1991.
Zheng Qinwen (19) 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, who reached the fourth round at Roland-Garros earlier this year, next faces Karolina Pliskova (30), who fired down 10 aces on the way to a 6-1 6-7(9) 6-3 win over Greek powerhouse Maria Sakkari (27).
American seventh seed Pegula rallied to beat Italy's Giorgi 3-6 6-0 7-5 and will next face Yulia Putintseva (27) after the Kazakh beat Alison Riske-Amritraj 6-3 7-5.