Qualifier Varvara Lepchenko shocked the reigning Roland-Garros champion while 37-year-old Venus Williams got off to another shaky start in the opening round at the WTA hardcourt tournament in Toronto on Monday.
Lepchenko rallied to stun French Open winner Jelena Ostapenko 1-6, 7-6 (7/2), 7-6 (7/5). Ninth seeded Williams also needed three sets and close to two hours to eliminate qualifier Irina-Camelia Begu 6-1, 3-6, 6-3.
American veteran Lepchenko, 31-years old and ranked 68th in the world, trailed 6-1, 3-0 before turning things around against the 12th-ranked Latvian, who had followed up her French Open triumph by reaching the quarter-finals at Wimbledon.
"I think I woke up, I was a little bit in the sleeping mode for a set and a half," said Lepchenko, a former top-20 player herself. "All the credit to her, she played amazing tennis - she hardly missed any ball from the very beginning.
"Once I gave her a little push back, that's when the game started. I pretty much focused on my game.
"I know I have powerful shots and I'm as good a player as her, so I knew I just had to give my best, and it would be a battle."
Lepchenko notched her first win this season over a top-20 player and her first since she beat then 15th-ranked Timea Bacsinszky at the US Open last year.
The match was one of the Centre Court highlights on the opening day of this key US Open tuneup.
Seven-time Grand Slam champion Williams, who is the oldest player in the draw, faced a stern test from Romanian Begu, who is ranked 59th in the world.
Heading into Monday's match, Williams had lost five out of seven opening-round matches in the event, which switches back-and-forth between Toronto and Montreal each year.
This marked the first career meeting between the two. Begu had already won a tournament in 2017 at Bucharest, while Williams, who finished runner-up in this event in 2014, is looking for her first title of the season.
Williams won the one hour, 56 minute match despite hitting no aces and making 10 double faults compared to her opponent's four aces and six double faults.
But Williams won 68 percent of her first-serve points and was able to break Begu's serve five times.
Williams advances to the second round where she will face either another qualifier Mariane Duque-Marino or world number 40 Katerina Siniakova.
Elsewhere, two-time Wimbledon winner Petra Kvitova, seeded 14th fended off Spain's Carla Suarez Navarro 6-1, 7-6 (7/5).
Kvitova breezed through the opening set, but had to battle back from 1-4 down in the second to finish off the Spaniard in straight sets.
Pliskova gets bye
Top seed Karolina Pliskova and second-seeded Simona Halep -- who won the Canadian crown last year when the WTA played in Montreal -- were among the top eight players enjoying first-round byes.
In other early action, Czech Barbora Strycova upset 13th-seeded Kristina Mladenovic of France 6-2, 6-3.
Strycova, ranked 26th in the world, raced to a 5-0 lead in the first set as Mladenovic struggled to find her rhythm.
Although Strycova was broken the first time she served for the set, she finally served it out with a love game and quickly took a 4-0 lead in the second frame.
She again turned back a late challenge from Mladenovic, who cut the deficit to 4-3 but was unable to convert three break points that would have seen her level the set.
It was another disappointing Canadian outing for Mladenovic, who has never won a match in Montreal or Toronto.
Elsewhere, British qualifier Heather Watson bowed out early, retiring while trailing Japan's Naomi Osaka 6-1, 4-1 with a shoulder injury.
Belgium's Kirsten Flipkens was up 6-2 when Croatian opponent Ana Konjuh retired, the victory sending Flipkens into a second-round clash with fourth-seeded Wimbledon champion Garbine Muguruza of Spain.