Andreescu gave Serena a long hug at the net where the American broke down after deciding she would find it hard to continue. She ended on an optimistic tone, saying that despite it being a rough year professionally, she was going to keep going and competing.
"I´m sorry I couldn´t do it today", Williams told the crowd, her voice cracking. But I just I couldn't do it. Thanks to Jehovah for letting me come out here.
"Bianca, you're a great sportsperson", she added. "I'll be back next year with new knowledge to approach important matches", said Medvedev after the match.
"It's not the way I wanted to win, but a win is a win". She withdrew from this week's Western & Southern Open at Cincinnati to give herself time to recover after dealing with shoulder and groin injuries this year.
"I really hope that I can crack the top 10 now and play in the WTA Tour finals by the end of the year".
Williams, who came in second place in the Wimbledon final last month, complained of back spasms and pulled out of the tournament in Toronto. (Laughs) It was nice, I guess, that I was injured during the summer because all my friends are in college right now - so I guess that was kind of good timing?
After talking to the physio it was announced Williams would no longer be able to continue and Andreescu walked over and embraced her distraught opponent.
And on Monday, she will move into the top 20 of the WTA rankings at world No 14.
There is no word yet on how severe Serena Williams back injury is or when she will be back on the court.
Unfortunately, his win wasn't enough to help Ulster lift the trophy as Leinster went on to win the men's doubles and retain the title by a single point, despite a subsequent victory for the McCullough twins Annie and Caitlin in the ladies doubles.
The 21-year-old from Hillsborough defeated Leinster's current worldwide Osgar O'Hoisin 1-6, 6-4, 6-2 as Ulster drew 3-3 with the hosts in their final match. "Tennis wasn't the most important thing for me", Murray said.
Andreescu brought her drop shot back against Kenin after rarely employing it against Pliskova.
Serena Williams had to bow out of the Rogers Cup tournament two weeks before the U.S Open.