Venus Williams prevailed in a three-setter but French Open champion Jelena Ostapenko and 13th seed Kristina Mladenovic crashed out of Rogers Cup with first round defeats on Monday.
Williams outlasted a lengthy rain delay and pesky Romanian opponent Irina-Camelia Begu to win her opening match 6-1, 3-6, 6-3.
Less than a month after her run to the Wimbledon final, where she lost to Spain's Garbine Muguruza, 37-year-old Williams again had to turn back time against a young challenger.
After taking the opening set in dominant fashion, the American found herself in a fight as Begu rallied back to win a set before rain suspended action for more than an hour.
The decisive set was a rollercoaster with Williams moving ahead 3-1 only to lose consecutive games before bouncing back to seize three straight games and the match.
Earlier, Mladenovic was swept aside 6-2, 6-3 by Czech Barbora Strycova while Ostapenko fell to American Varvara Lepchenko as upsets marked the start of the tournament.
Strycova's stunning triumph was followed by another surprise victory when 12th seed Ostapenko lost 1-6, 7-6(2), 7-6(5) to American Lepchenko in two hours and 36 minutes.
After breezing through the first set, the 20-year-old Ostapenko's nerves began to show and unforced errors helped Lepchenko, 31, take the final two sets in tiebreaks.
Fan favourite Petra Kvitova, determined to improve following a knife injury to her hand inflicted by an intruder at home, beat Spaniard Carla Suarez Navarro 6-1 7-6(5).
The Czech’s six aces and 32 winners were too much for the 28-year-old Navarro, who had no aces and just seven winners.
"I'm feeling pretty tired right now," said Kvitova, who was trailing 4-1 in the second set before winning the tiebreak.
"I'm trying to come back as soon as possible but it is just a matter of time," added the 14th seed.
Hip holds as Kyrgios rolls on at Rogers Cup
Temperamental Australian Nick Kyrgios looked fresh and focused as he blazed to a 6-1, 6-2 first round win over Viktor Troicki at the Rogers Cup in Montreal on Monday but warned he was rolling the dice with a hip injury that could flare up at any time.
The wobbly hip that hit Kyrgios's grasscourt season, with first-round retirements at London's Queen's Club and Wimbledon, have followed him into the North American hardcourt season.
But the 16th seed showed no signs of distress in dispatching Troicki after 51 minutes on a sun-kissed centre court.
"I'm feeling it all the time," said Kyrgios.
"It's not something that is just going to heal. I can compete so that's the most I can do at the moment."
With his mother watching from the stands, the hot-headed Australian kept his cool against an overmatched opponent who has been struggling with his own injury issues.
Tennis fans never quite know what to expect when Kyrgios steps onto the court.
On opening day, at least, the fans saw a motivated Kyrgios playing near his best and treating the crowd to a display of power and finesse.
The only lapse in an otherwise dominant effort was Kyrgios's inability to deliver the knockout punch with the 22-year-old needing seven match points to finish off the 45th ranked Serb.
In later games, Juan Martin del Potro withstood 24 aces from John Isner to knock off the big-serving American 7-5, 7-5. Del Potro, a 2009 finalist at Montreal, broke Isner’s service while tied at 5-5 in both sets to advance. Isner had been red hot after capturing back-to-back tournaments in July.
Roberto Bautista Agut rolled past Tim Smyczek 7-6(4), 6-1,while American Jared Donaldson, 66th in the world, provided the first upset of the tournament by knocking out French 13th seed Lucas Pouille, twice a title winner this season, 7-6(5), 7-6(8).