Serena Williams retired with a back injury in the final of the the Rogers Cup in Toronto, handing the title to Canadian teenager Bianca Andreescu.
Williams, 37, was left in tears after suffering back spasms as 19-year-old Andreescu comforted her courtside.
The American was a break down in the first set when she withdrew.
"I'm sorry I couldn't do it today, I tried," said 23-time Grand Slam champion Williams. "It's been a tough year, but we'll keep going."
Andreescu, who won her first WTA title at Indian Wells earlier this year, becomes the first Canadian to win the Rogers Cup women's singles title since 1969.