The third-seeded Sharapova, who can seize the world's top ranking from Victoria Azarenka depending on results this week, was demolished 6-0 6-1 by Williams in London but said the loss will motivate her ahead of the August 27-September 9 U.S. Open.
"If I sat here and thought there was nothing I could do, that would probably be very disappointing," Sharapova said.
"It will motivate me to keep going and keep practicing. There are certainly things I could have done better but she was playing really good tennis."
The Olympic silver medallist, who completed her collection of grand slam trophies with her French Open triumph in June, is among a host of top players the $2 million Montreal tournament, which is considered a key lead-in event for the U.S. Open.
Williams, who defeated Australian Sam Stosur when the event was played in Toronto last year, is the only top-10 world ranked woman not playing in the Aug. 4-13 Montreal event.
Stosur, who avenged her Toronto loss to Serena Williams with a victory over the American in last year's U.S. Open final, said the absence of the Wimbledon and Olympic champion is not a bad thing for the rest of the field given her recent form.
"I don't think anyone is that worried about not playing them," Stosur said. "(Serena) is breaking lots of records, which is great for our sport, but we are not going to complain if we don't have to play them all the time."
While the 16 seeds in the 48 player draw received first-round byes, Italian Roberta Vinci started play in the main draw by posting a 6-2 3-6 7-5 win over Belgian Yanina Wickmayer.
After winning the first set comfortably, Vinci struggled with her opponent's more powerful ground strokes and was on the verge of defeat when trailing 5-1 in the final set.
Instead it was Wickmayer who lost her composure, initially when serving a double fault on match point and later when losing her temper as the Italian gained momentum.
Vinci now plays the 11th-seeded Ana Ivanovic.
- Serena Williams