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

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."