"It wasn't that my level went down tremendously, it was literally one or two points which made a huge difference in that second set". She had to survive upset-minded Kanepi, who knocked off No. 1 Simona Halep in the first round and stormed back from being bageled in the first set to seize the second.
She was stretched the distance for the first time this fortnight, but Serena Williams found a way.
"I was just living in this world where I thought it would just automatically come together", said Williams, who is just seven events into her comeback that began in March in Indian Wells.
Williams finished with a tally of 47 winners, including 18 aces.
But Kanepi held firm and took the 23-time Grand Slam champion into a decider.
"Not only that, mentally and physically and dealing emotionally with providing for another child, it's a lot that goes into it", she said. "I'm just happy to get through it, to be honest".
Williams reached the quarterfinals at Flushing Meadows for a 10th consecutive appearance - she wasn't there a year ago because she gave birth to her daughter during the tournament - by picking her level up after a lull and using 18 aces to beat Kaia Kanepi of Estonia 6-0, 4-6, 6-3.
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But in this kind of match, usually you can win in the last 20-25 minutes. "I was really pleased to progress in the Carabao Cup". If he improves that, he could be the best left-back in the world".
Pliskova defeated Williams in the semi-finals in NY in 2016.
"Obviously it won't be easy", she said. Being defending champion, being able to get to the quarter-finals again, is incredible.
'Life hits you and you think, "What about me?"
Williams's fellow American John Isner booked his trip to the quarterfinals in the men's draw Sunday, defeating No. 25 seed Milos Raonic, 3-6, 6-3, 6-4, 3-6, 6-2, in Louis Armstrong Stadium. Then she lobs me to my forehand.
Kanepi turned things around early in the second set, as Williams' serve speed dropped and Kanepi picked up her level.
Plislkova's runner-up finish to Kerber in the 2016 US Open remains her best Grand Slam finish, but Williams noted she briefly gained the number one world ranking past year.
Recalling her 2017 quarterfinal victory over Sevastova, which was decided by a third-set tiebreaker, Stephens said- "I had to dig really deep". "It will be an interesting match". "I'm feeling great now, too, but it was a little bit different story, 2016", Pliskova said Sunday. She hasn't won since and is trying to avoid going without a Grand Slam for the first year since 2011. I have a good serve. "I feel like it's important for women to know that it doesn't happen like [it looks] in the Instagram world". "There is always a chance for me".
Williams, chasing a record-equaling 24th grand slam, is playing her seventh tournament - and a third grand slam - since giving birth to daughter Olympia last September.