Mauresmo hadn't played since Wimbledon.
Maria Sharapova looked impressive in a 6-3, 6-4 win over No. 10 seed Nadia Petrova in a night match. Sharapova broke Petrova once in the first set and twice more in the second to run her record to 8-1 against her fellow Russian opponent.
No. 13 seed Marion Bartoli was also eliminated with a 6-4, 6-3 loss to Alona Bondarenko, who is ranked 33rd.
The first round also wiped out most of the Canadians in the field, leaving only Quebec's Aleksandra Wozniak in the tournament.
Fellow Canadians Stephanie Dubois, who reached the third round of this tournament in 2006 and 2008 when it was played in Montreal, Heidi El Tabakh, and Valerie Tetreault, all lost Monday at the Rexall Centre.
The 22-year-old Dubois, ranked 112th, double-faulted three times in the opening game of her match against Roberta Vinci and lost 6-1, 6-2.
The 194th-ranked El Tabakh took 17th-ranked Samantha Stosur to two tiebreakers but lost in straight sets 7-6 (2), 7-6 (4).
Tetreault was beaten 6-2, 6-4 by Agnes Szavay.
"I did great at the Rogers Cup for the past four years," Dubois said. "So this for me is a little bit disappointing."
Wozniak, Canada's top-ranked women's player, will meet Alisa Kleybanova on Tuesday.
Dubois, who reached the second round in 2007 when the event was held in Toronto, had her serve broken seven times by Vinci.
In other matches, Ai Sugiyama defeated Iveta Benesova 6-3, 6-4; Aravane Rezai beat Alize Cornet 6-4, 7-5; Kateryna Bondarenko topped Yanina Wickmayer 7-6 (4) 6-2; Sybille Bammer eliminated Anna Chakvetadze 3-6, 6-4, 6-2; Agnieszka Radwanska knocked off Carla Suarez Navarro 6-3, 6-3; and Patty Schnyder defeated Anabel Medina Garrigues 6-2, 6-1.
Beck, Daniel advance to Swiss Open semifinalsToffees show Lescott love
