Bouzkova, 21 and ranked 91st in the world, had said it was a dream come true to take on 37-year-old United States superstar Williams, and she made a dream start - breaking Williams three times to take the first set in less than half an hour.
Having suffered two Grand Slam final defeats, Williams will go in search of her 24th major title in NY next month, while Osaka will look to defend her crown after early exits at Wimbledon and the French Open.
"We haven't played since NY which was a really good match for her and I just wanted to come out and try to win a set this time because she's beaten me twice so I just wanted to do the best I could today", Williams said in an on-court interview.
Serena Williams survived a scare before getting past Marie Bouzkova in the Rogers Cup semi-finals on Saturday.
"I can't really let what other people say affect me, and I just have to keep working hard and putting effort". "In the third set I told myself, 'Go big or go home, '" the home hope said.
A win for Williams sees her bounce-back after losing in disastrous conditions at the Arthur Ashe Stadium in NY, when the 37-year-old received code violations for coaching, smashing her racket, and calling the umpire Carlos Ramos a "thief" at the 2018 US Open. I go into every match thinking I can do it, but sometimes that doesn't happen.
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The Czech Pliskova had a chance to overtake Barty and Osaka had she reached the final.
"And, actually, this is how I thought the first time I played her in Miami was going to go".
"So in a weird way, losing today I accomplished my dream", she said, according to CNN. Williams spoke about the turnaround: "I just needed to be more consistent and not make so many errors and just mentally be ready to hit a thousand balls if I needed to".
But the 19-year-old, who shot to prominence with her Indian Wells triumph in March, went toe-to-toe with her more experienced opponent to win by serving out to love.
"I'm glad it was two sets today, but it wasn't easy".
"We haven't played since NY, which was a really good match for her". Nadal has 82 singles victories, winning the French Open in June for his second title of the year.