Not only has the teenager become Canada's first Grand Slam singles champion, but she is also the youngest Major victor since Svetlana Kuznetsova won the 2004 US Open, when the Russian was also 19 years old.
The 19-year-old's triumph, which came in her US Open main draw debut and against the undisputed queen of the sport, was the latest step in a meteoric rise for Andreescu and it dominated front pages across the country.
"I believe I could have just been more Serena today", said Williams, a six-time champion at Flushing Meadows. "Oh, man, it wasn't easy at all".
Williams, who remains one Slam title shy of matching Margaret Court's all-time record, has lost the past two Wimbledon and US Open finals since returning after having a baby two years ago. She became the first Canadian to reach a Grand Slam finals. Her victory at the US Open will bring her to 5th place in the WTA ranking of the best women's tennis players in the world. She was ranked 208 last summer.
When Andreescu faced Williams inside Arthur Ashe Stadium she was cheered on at viewing parties across her home country, the type normally reserved for events like Olympic ice hockey finals featuring Canada but never before for tennis. Her risky coin-toss choice to receive against a master server ended up in her favor.
"Serena will be looking at it, 44% of first serves in, and that's not good enough", Barker said.
In the second set, Williams began to turn over her game.
After the victory, Andreescu reflected on what she accomplished. I know they can't always travel.
"I feel like, in 20 years, I definitely will be like, "Wow, that wasn't so bad", the 37-year-old Williams said, her words halting, her voice scratchy.
She added: "I was just fighting at that point, trying to stay out there a little bit longer".
For a spell in the second set, Williams took the initiative against Andreescu, who let a 5-1 lead and championship point slip away.
"My team has been so supportive through all the ups and downs and downs and downs and downs and downs and downs.Hopefully we'll have some ups soon".
Andreescu won at Indian Wells and in the Rogers Cup, too, and reached a career-high number five in the WTA rankings on Monday following her NY success.
Williams has previously described herself as a fan of Andreescu and acknowledged that, with the exception of sister Venus, there is nobody she would rather lose to.
Both attribute their success to a strong mental game as much as a physical one. Andreescu has spoken about her pregame meditation ritual. The Canadian, speaking in a press conference, said: " Andreescu spoke of her idols: "Bassett, for sure, was very inspirational.
"It's definitely frustrating. But for the most part I just am still here".