Three-times winner Serena Williams moved into the Toronto Open second round with a 6-3, 6-4 win over Spain's Nuria Parrizas Diaz on Monday while Wimbledon champion Elena Rybakina and Simona Halep also advanced.
Williams, in only her second singles match since returning to action at Wimbledon in June after a year-long absence from competition, was forced to dig deep during a nearly two-hour match played in hot and humid conditions.
"Mentally I feel I'm getting there. I'm not where I normally am and I'm not where I want to be," Williams told reporters.
"Physically I feel much better in practice, it's just like getting that to the court. But literally I'm the kind of person who it just takes one or two things and then it clicks. So I'm just waiting on that to click."
One of 14 major winners in the main draw of an event that is a tune-up for the US Open, Williams clinched the opener on her fourth set point with a vintage smash that Parrizas Diaz had no chance of returning.
The second set was a much tighter affair and Williams did well to hold serve in a physically demanding 18-minute game during which she fought off four break points to get to 4-4 before sealing her first singles win since the 2021 French Open.
"It's just one win, you know, it takes a lot. But I was happy, like I said, to have a win," said Williams. "It's been a very long time. I forgot what it felt like."
Up next for Williams will be either Olympic champion Belinda Bencic, the 12th seed, or Czech Tereza Martincova.
Romanian 15th seed Halep, who retired from her second-round match last week in Washington due to illness, needed just 61 minutes to secure a 6-0, 6-2 win over Croatia's Donna Vekic.
The twice Canadian Open champion breezed through the first set in 21 minutes and never looked back as Vekic grew more frustrated as the match wore on.
"It's not about the result it's more about how I played," Halep, who did not face a break point, said during her on-court interview. "I've been very aggressive and I played fast so that's my goal and I am trying to do that every day."
Kazakh Rybakina, who followed her Wimbledon triumph with a first-round exit at San Jose last week, beat Czech Marie Bouzkova 7-5, 6-7(3), 6-1 for her first win as a Grand Slam champion.
Czech 14th seed Karolina Pliskova and Latvian 16th seed Jelena Ostapenko also advanced while Sloane Stephens was leading Sofia Kenin 6-2, 6-7(5), 1-0 on centre court when play was suspended due to rain.
Canadian 13th seed Leylah Fernandez will kick off the night session in Toronto against Australian Storm Sanders before Venus Williams meets Switzerland's Jil Teichmann.
Wawrinka and plenty of rain fall at Canadian Open
Stan Wawrinka's attempts to get his comeback season off the ground took another hit on Monday as the three-time major champion fell 6-3, 3-6, 6-3 to Emil Ruusuvuori in the rain-delayed opening round of the Canadian Open in Montreal.
Wawrinka, 37, missed the clay, grass and hardcourt season last year following surgery on his left foot and since returning in March has suffered a slew of first round exits.
The Swiss former world number three played solid tennis but was unable to overcome hard court specialist Ruusuvuori, who smashed a forehand winner on match point to advance.
Next up for the Ruusuvuori is a second round clash with Hubert Hurkacz, who the Finn defeated in Washington last week for the biggest win of his career.
Karen Khachanov came out on the winning side in a sloppy three-set match against Francisco Cerundolo, where the players made a combined 110 unforced errors compared to just 45 winners.
The Russian has played well at the tournament in the past, reaching the semi-finals in 2018 and 2019.
In other first round action, 21-year-old American Jenson Brooksby made quick work of Alexander Bublik with a 6-2, 6-3 win and Slovak Alex Molcan outlasted Mackenzie McDonald 7-6(1), 6-4.
Heavy rain delayed the start of the Masters 1000 tournament for hours and forced the postponement of Andy Murray's highly anticipated first round match against Taylor Fritz to Tuesday.