NEW YORK -- Before the U.S. Open began, Patrick Mouratoglou predicted Bianca Andreescu would be in the final.

He was right.

Serena Williams's coach also is confident the rising Canadian tennis star will be No. 1 in the world one day. He may well be right about that, too.

But on Saturday, when Williams meets Andreescu in the women's singles final, he considers the 23-time Grand Slam champion he's been guiding since 2012 to be the favourite.

"I'm not surprised (Andreescu) is there. I expected her in the final, and I think she's going to be No. 1 in the future, because she has everything that's needed to be No. 1. A lot of respect for her," Mouratoglou said some 24 hours before the 37-year-old Williams and the 19-year-old Andreescu square off in the final.

"A lot of tools in her game -- like, a really complete game. She has the whole package. The game's amazing, I think: the athleticism, and the mental. She looks incredibly confident. She feels like she's where she belongs. That's the impression she gives."

Sylvain Bruneau, Andreescu's coach, said his player will have to play a near-perfect match on Saturday.

"She'll have to do everything well. Serve well, Return well. Play well from the baseline and keep the ball deep, and move Serena around," Bruneau said. "Vary the rhythm. Play a complete match.

"It will take a great performance, that's clear," he added.

There are 18 years and 263 days between Williams and Andreescu. It's the largest age gap between Grand Slam finalists in the sport's Open era, which began 50 years ago.

Williams won her first U.S. Open as a 17-year-old in 1999, almost exactly nine months before Andreescu was born.

Her career won-loss record at Flushing Meadows is 101-12.

Andreescu's career record, on the other hand, is 6-0. She's making her first main-draw appearance at the final Grand Slam of the season.

Notably, though, the Canadian is 7-0 against top-10 players in 2019. Williams is currently ranked No. 8.

If she wins, Williams would move up to No. 6 in the rankings. If Andreescu wins, she would be No. 5 -- less than 50 points behind the No. 4 player, who will be 2018 champion Naomi Osaka.

If the Canadian is beaten, she still will make her top 10 debut on Monday, at No. 9.

"We're trying to stay in the daily routine, what we've been doing since the beginning of the tournament," Bruneau said. "I'm happy that she was able to play Serena in Toronto, even if it was only for four games (in the Rogers Cup final before Williams retired with a back injury last month). I think the experience of preparing for that ­-- it was in Toronto, so it wasn't the U.S. Open experience, but it was far from an average WTA Tour event -- there were some similarities."

As coaches, Mouratoglou and Bruneau couldn't be more different. Mouratoglou is a larger-than-life personality, a television analyst in two languages and a tennis academy owner who embraces the spotlight that comes with coaching one of the greatest players in tennis history.

He came through the private sector to the top of tennis, while Bruneau rose through the ranks in Tennis Canada, the national federation for whom he's worked nearly his entire career. He's been a low-profile player and happy that way -- until Andreescu's rise suddenly shone the spotlight on him.

And unlike Mouratoglou, for whom this is old hat, Bruneau is every bit the Grand Slam final rookie his charge is.

"We're in situations right now in which I don't have much experience. It's the first time for me, too, that I'm the coach of a player who's in a Grand Slam final," Bruneau said. "In 2014 I was around Eugenie Bouchard during the year she played very well. I learned a lot then. And I think it's prepared me for what's going on now."

Mouratoglou said it was far too early in Andreescu's career to compare her to Williams. But he praised her skills as a competitor.

"The best players in the world are the best competitors. So if (Andreescu is) at that level now, and at 19 she's in a Grand Slam final, it's because she's a great competitor," he said. "We'll see what she'll do in her career. But all you have to do is look at her head-to-heads against the top 10 -- and see she's never lost to a top 10.

"She doesn't need -- as others do -- to reassure herself that she can do it, to only then be able to do it. She just does it," he added.

"That's the sign of someone who beyond being a great competitor, has tremendous confidence in herself as well."

Bruneau is trying to keep to the same routine. But of course, nothing is routine about a Grand Slam final.

"It's not just another match, but we will try to pretend it's just another match. Obviously she has a legend against her on the other side of the court, but that should not change what she has control over. I think that's going to be the message," Bruneau said. "My goal for her tomorrow is that she be free on the court, play her tennis, go for it -- and we'll see what happens."