Williams was under pressure from the start as she survived break point in the opening game of the match before Andreescu surged into a 3-1 lead inside 19 minutes.

However, the American was unable to continue as she returned to her chair after the fourth game and was forced to retire due to an upper back injury, which saw the 37-year-old reduced to tears.

Andreescu consoled Williams after her retirement was confirmed as the emerging teenager lifted her second title of the campaign in front of her home crowd.

There has not been a home winner of the event – which first took place in 1892 – since Faye Urban defeated Vicki Berner in an all-Canadian final in 1969.

Andreescu, reported on wtatennis,com, said on court: “I’m speechless right now. I’m the first Canadian to make the final and win this tournament since 1969.

“This week has not been easy, I’ve had many many tough matches, and especially what I’ve been through the last two months hasn’t been easy. I kept telling myself never give up.”

Andreescu – who was born in Thornhill, which is situated less than 15 miles north of Toronto – was making her first appearance since the French Open second round due to a right shoulder injury.

The 19-year-old, who defeated two top-10 players en route to the final, will break into the world’s top 20 for the first time in her career on Monday.