Venus Williams avoided an upset at the hands of fellow American Caroline Dolehide, holding off the 19-year-old 7-5, 6-1 to claim her first round match at the Rogers Cup on Monday.
Williams, coming off a disappointing quarter-final loss at the Silicon Valley Classic last week, fell down a break early but recovered to turn back her dangerous opponent.
"I think she had a really great second serve," Williams told reporters, of Dolehide.
"I think I got a better feel for it in the second set. In the first set, I was still figuring it out."
Dolehide displayed her full potential in March when she nearly took down world number one Simona Halep at Indian Wells. Against Williams, the young player lost momentum late as Williams claimed 12 of the final 14 games of the match.
The only two other seeds in action during the opening day were ninth seed Karolina Pliskova and 10th seed Julia Goerges who both won.
Pliskova beat Katerina Siniakova 6-4, 6-4 while Goerges overcame Timea Babos 3-6, 7-6(3), 6-4.
Among those yet to play are top-ranked Halep and number two Caroline Wozniacki of Denmark. The top eight seeds all received first-round byes.
Raonic advances, Sock ousted in Rogers Cup
Canadian Milos Raonic made good use of his booming serves to oust 10th seeded Belgian David Goffin in the first round of the Rogers Cup on Monday.
Playing in front of fellow Canadians in Toronto, Raonic topped Goffin 6-3, 6-4, winning all 27 of the points scored while he was on first serve.
"I think I can still serve much better," Raonic told reporters after needing only 73 minutes to advance. “The way I was aggressive from the baseline, I hit my forehand well. It's something we spent these last two weeks working on."
The unseeded Raonic, who is coming off a run to the quarter-final at Wimbledon, will next face the winner of Tuesday’s match between American Frances Tiafoe and Italian Marco Cecchinato.
Thirteenth seed American Jack Sock suffered a defeat to Russian qualifier Daniil Medvedev 6-3, 3-6, 6-3. Medvedev will play the winner of Canadian Felix Auger-Aliassime and France's Lucas Pouille in the second round.
Eleventh-seeded Diego Schwartzman of Argentina and 12th-seeded Pablo Carreno Busta were also first-round winners.
Spain's Rafael Nadal is the top-seeded player in the tournament, while Germany's Alexander Zverev, who won the Citi Open championship on Sunday in Washington, is the second seed.