US Open champion Andreescu's tearful response after Serena win

As the enormity of what she had achieved washed over her, Bianca Andreescu finally gave in to her emotions.

Andreescu's teenage tears of joy

The 19-year-old Canadian has been the definition of composure, laser focused on one goal – winning her first grand slam title at the US Open in her main draw debut.

However, having achieved that dream by stunning Serena Williams and denying the American great a record-tying 24th grand slam with a 6-3 7-5 victory at Flushing Meadows, she allowed that composure to slip.

Andreescu sank to the court in what looked to be a combination of relief, disbelief and exhaustion after completing her triumph and in her post-match media conference she broke down while reflecting on what the success meant to her.

Asked how she visualised the match going, a tearful Andreescu replied: "This wasn't the only time I visualised playing in the finals actually against Serena Williams. It's so crazy, man.

"I've been dreaming of this moment for the longest time. Like I said after I won the Orange Bowl [at age 15], a couple months after, I really believed that I could be at this stage.

"Since then, honestly I've been visualising it almost every single day.

"For it to become a reality is just so crazy. I guess these visualisations really, really work."

Andreescu conceded she did start to doubt herself as Williams, backed by a deafening crowd desperate for her to tie the record, roared back from 5-1 down to level the second set at 5-5, a fightback she was in no way surprised by.

"I had some doubts because I've witnessed her come back from being 5-0 down, 5-1 down, 5-2 down. I just told myself to stick with my tactics," added Andreescu.

"She started playing much better. I think the crowd really helped her, as well.

"I was blocking out the noise, or trying to. I could barely hear myself think really. It was really, really loud. But I guess that's what makes this tournament so special.

"It definitely wasn't easy, especially when she started coming back in the second set. I mean, it was expected. She's a champion. That's what champions do. She's done that many, many times throughout her career.

"But I just tried to stay as composed as I could. It's hard to just block everything out, but I think I did a pretty good job at that."