TORONTO — Caroline Wozniacki's father used to tell her not to whine whenever she had to face an opponent with a hard serve during her junior career.
It could be worse, the then pre-teen Dane was told. It could be Serena Williams on the other side of the net.
Williams was already a force on the WTA Tour when Wozniacki turned pro in 2005 — with seven of her now Open Era-record 23 Grand Slam championships under her belt by that point. When it came time for Wozniacki to face her idol for the first time a few years later, she quickly realized what her father meant about that powerful serve.
Playing Williams, Wozniacki says, has always been a learning experience. And the biggest lesson?
"I've learned that I would like to be on the other side of the draw," Wozniacki said with a smile.
"But, no," she continued. "It's always fun to play someone who is the best ever to play the game. You learn a lot every time, and we've played against each other quite a lot.
"Obviously she always pushes you to play your best tennis. And you have to serve and you have to return well to have a chance, and then you just have to keep your head down and keep playing."
Wozniacki and Williams became close friends years ago, and Williams even served as one of Wozniacki's bridesmaids at her wedding earlier this summer.
But that familiarity hasn't given Wozniacki any advantage over Williams on the court. The 29-year-old has just one career win in 11 meetings against the American superstar.
Williams, competing at the Rogers Cup this week for the first time since 2015, plays Elise Mertens of Belgium at Aviva Centre in her opening match on Wednesday after getting a first-round bye.
The longtime No. 1 entered the Toronto tournament ranked ninth in the world, her highest claim on the WTA leaderboard since taking 14 months off after her 2017 Australian Open title to give birth to her daughter, Olympia.
While she has yet to win a tournament since returning to action last March, Williams is poised to break through once more, with a pair of Grand Slam finals appearances helping prove she's back to form.
The players who beat her in those majors look to those victories as crowning achievements — not only to win a Grand Slam title, but to have to go through Williams to do it.
"We all grew up watching her," said 21-year-old Naomi Osaka, who beat Williams in the 2018 U.S. Open final. "Every tennis player has that competitive edge where we want the chance to play her. And she's literally the best.
"In tennis I feel like if you want to prove something, especially if you're young and coming up, you want to play the better players and you want to show them what you can do. So for me, that was definitely the case."
The No. 2-ranked Osaka said she didn't think about Williams's massive list of achievements when she stepped onto the court against her last September, preferring to "live in the moment" instead.
Simona Halep took a similar mental approach when beating the 37-year-old in the Wimbledon final last month, their 11th all-time meeting.
The defending Rogers Cup champion improved to 2-9 against Williams with that victory, but just forcing a third set in four of her nine losses helped convince her she's not too far off from Williams's level.
Halep still described beating Williams for the Wimbledon title as "the best day," though.
"It's tough to have a good record against Serena so I didn't really think about that before the match," the No. 4-ranked Romanian said. "I had in my mind that I beat her once ... and I knew if I played my game then I'd have a chance to win.
"The game, in my opinion, was perfect."
Current world No. 1 Ashleigh Barty of Australia (0-2 against Williams) said she was much more intimidated the first time she faced Williams, summing up the experience in one word — "terrifying."
Barty was just 17 at the time and playing Williams in a first-round match under the lights at Rod Laver Arena at the Australian Open.
"For me that was probably one of the biggest moments in my career ... An incredible moment, it really was," Barty said of the 6-2, 6-1 loss. "Just being on the other side of the net from Serena for the first time was crazy, it was bizarre.
"I feel like I learned from that match. That's what I try to do is learn from every experience."
Wozniacki maintains that Williams can be the best teacher for any tennis player — and the best test of anyone's abilities.
She'd just prefer not to get to that test too early in a tournament.
"You always want to play the best players in the game and you want to have that experience to measure yourself up against them and know what you need to do to get there," Wozniacki said.
"But once you've done that, you want to go far in tournaments. And you want to play the best players as late as possible."
Melissa Couto, The Canadian Press
