Sylvain Bruneau didn't even hesitate when asked whether he thought his student, Bianca Andreescu, would reach such great heights in tennis so quickly.

"No."

So how then did the 19-year-old Mississauga, Ont., native, who was ranked 152nd at the beginning of this season, manage to capture two titles, including a Grand Slam, and climb to No. 5 in the WTA rankings in a breakout season that has turned her into a household name?

"She's done what's she done by being focused, hard working," Bruneau, her full-time coach since 2018, said Tuesday in Montreal.

Bruneau, who is based in Montreal, is back from New York City, where Andreescu won the U.S. Open on Saturday to become the first Canadian player to win a Grand Slam singles title.

"She's won her first Grand Slam, and she's already said loud and clear she wants to win more."

Bruneau, centre, has guided Andreescu to the biggest achievement in Canadian tennis history. (Elsa/Getty Images )

Despite basically missing four months due to a shoulder injury, so far this year she has won more prize money (more than $6 million US) than any other female player, and has tied for the most tournament wins with three.

Andreescu, who now lives in Thornhill, Ont., appeared on several U.S. TV shows, including Good Morning America and The Tonight Show on Monday.

She returns to Canada on Wednesday and will be in Montreal next week to resume training ahead of a tournament in China.

An 'unbelievable connection'

Bruneau has known Andreescu since she was around 15 due to his previous coaching roles, including serving as Fed Cup captain.

He became her personal coach in March 2018. Since then, the pair have forged an "unbelievable connection.

"We've connected really, really well, and I think ... that's very important for any player, to have that kind of connection with their coach where they feel they can share everything."

Watch as Bruneau gives Andreescu a pep talk earlier this year:

Andreescu's 3rd set conversation with coach Sylvain Bruneau was the turning point in her match as she went on to break the next game and eventually win her 1st career WTA title. 1:07

He said the two of them have a "move" they shared when she won her matches during the U.S. Open — something he said it doesn't appear anyone has noticed, but is an example of their ability to have fun together.

Facing Serena

Andreescu is the first woman to win the title in her U.S. Open debut and the first player born in the 2000s to win a tennis Grand Slam.

To do that, she had to beat Serena Williams, one of the best tennis players of all time, the crowd favourite and maybe, most importantly, one of Andreescu's idols.

Bruneau said part of Andreescu's preparation to face Williams began at the Rogers Cup, where the two faced off in the final until Williams retired due to injury.

"If she stepped on that court being a little intimidated by Serena, and not totally believing she could do it, she wasn't going to do it."

At the U.S. Open, Andreescu had warmed up using the same practice court for the entire tournament. About 30 minutes before the final, her team caught wind that Williams was warming up in the same place, and they went to ask Andreescu if she wanted to practise somewhere else.

"I was like, 'No. No, no, no, we're not asking Bianca. She's warming up there, right beside Serena, because we spent a lot of time making sure she wasn't going to be intimidated, so we're not going to start right before the match.'"

This is the whole story of the practice court showdown:

Even before Bianca Andreescu and Serena Williams took the court for their U.S. Open title match, Andreescu's coach Sylvain Bruneau made sure she stayed on the same practice court, right next to Serena. 1:04

Bruneau said Andreescu's confidence grew steadily over the last year, starting in earnest with a win at the prestigious tournament at Indian Wells, Calif.

"It just snowballed. She got better results, and I tried to get her to believe there was no limit to what she could do. I think she, at some point, started to believe that."