Andreescu wins Toronto after Serena retires just four games in

Disappointed. There's no other word to describe how fans and Serena Williams felt on Sunday in Toronto. After just four games, Williams retired with an upper back injury while down 3-1 to Canada's Bianca Andreescu.

"I'm sorry I couldn’t do it today. I tried," Williams told the crowd in tears. "I just couldn’t do it. It’s been a tough year, but we’ll keep going."

Though it was a completely anti-climatic finale, Andreescu is officially the 2019 Rogers Cup champion, making her the first Canadian woman to win the title in 50 years. Williams' back pain started on Saturday when she needed three sets to get past qualifier Marie Bouzkova.

Andreescu can relate to the 37-year-old's injury struggles, having missed almost all of the last four months with a torn rotator cuff in her right shoulder.

"I know how it is to pull out of tournaments and be injured. It’s not easy," Andreescu told Serena. "This wasn’t the way I expected to win and for you to go off the court."

Since her out-of-nowhere win at Indian Wells, the 19-year-old entered just two events (Miami and Roland Garros) and didn't complete either one. Toronto was her first healthy tournament back and she beat Eugenie Bouchard, Daria Kastakina, Kiki Bertens, Karolina Pliskova and Sofia Kenin before her highly anticipated showdown with Williams.

"I'm speechless right now," Andreescu said. "I’m the first Canadian who got to the final and has won this tournament since 1969: This has been a dream come true. This week has not been easy. I’ve had many many tough matches, and especially what I’ve been through the last two months [has] not been easy, but I kept telling myself never give up."

The 2019 season has been a remarkable breakthrough for Andreescu. The teenager was ranked No. 178 at the start of the year, and needed a wild card to enter Indian Wells. She'll be ranked No. 14 in the world come Monday.

Meanwhile, Williams' health continues to hold her back, with her knee being most troublesome this season and now a new injury. She's still meant to play Cincinnati next week before heading to New York.