But a dream ending?
It took just 19 minutes for the 19-year-old to become the first Canadian in 50 years to capture the Rogers Cup.
Williams, who was looking to win her first tournament since returning after the birth of her daughter, was down a break in the first set, trailing 3-1, when she could not continue. She'll wake up tomorrow ranked 14th, the highest-ranked teenager on Earth.
"I'm speechless right now", Andreescu told the Aviva Centre crowd in Toronto during her celebratory ceremony on the court. "It was a bit sore, but I think it got a little bit worse during the match".
Of course, the crowds weren't the problem for the three-time Rogers Cup victor on Sunday. Serena was forced to pull the plug and remove herself from contention due to back spasms she was experiencing.
Andreescu will move from 27th to 14th in the world rankings after snatching her second WTA Premier title this season.
Williams delivered a tearful speech after the game, saying she was sorry she couldn't go on.
Andreescu doubled over in frustration when her perfectly lined-up forehand smash went long, returning the serve to Kenin and making the tiebreak 5-4.
"I'm not a crier, but, thank you guys", said Williams as she choked back tears after accepting the second-place check.
Later Friday, Bianca Andreescu of Mississauga, Ont., took on third-seeded Karolina Pliskova of the Czech Republic. She ended on an optimistic tone, saying that despite it being a rough year professionally, she was going to keep going and competing.
It's Andreescu's first tournament back from a right-shoulder injury that has sidelined her since the French Open in May. Andreescu is the first Canadian woman to win the Rogers Cup since Faye Urban in 1969.
So in case you were wondering, yes, it was deserving of all the hype. Serena has won six of her last eight matches on hard court.
"She's fearless on court", says fan Michelle Aristizaba, who's been playing tennis for more than two decades. Sixteenth-seeded Gael Monfils then withdrew before his semifinal against world No. 1 Rafael Nadal.
The US Open begins at Flushing Meadows two weeks from Monday. On the men's side, Milos Raonic retired after two sets against Felix Auger-Aliassime in a much-anticipated all-Canadian matchup. Andreescu asked, her care and concern so genuine.
Serena later explained to the Rogers Cup crowd that she simply couldn't tough it out that day, noting that she had tried.
Svitolina beat Caroline Wozniacki in the 2017 Rogers Cup final, the last time the women's half of the tournament was in Toronto. But the historic result is significant nonetheless.
Williams, 37, is a tennis juggernaut who was winning titles before Andreescu was even born.
Williams was certainly impressed, calling the Canadian an "old soul". Andreescu hugged her and told Williams how much she admires the 23-time Grand Slam victor.