So that was the good news. Then I thought to just try making less errors, because at that point I was missing a lot of shots.
"I just play them instinctively, and that's how they work, or don't work sometimes."
Indeed Stephens fought back to narrow the gap to 4-3, but Sevastova grabbed another break with a well-timed drop shot for a 5-3 lead and sealed the victory on her third match point when a tired Sephens put a backhand into the net.
"I had couple break points", Pliskova recalled after the match. "I think that was the biggest chance for the first set because with a double break, I would feel for sure less pressure on my serves".
But when she fell behind 0-40 in the seventh game she rescued herself with 112 miles per hour (180 Km/h) service victor followed by a another service victor and an ace.
"Somehow I just couldn't find my rhythm at all in the first set, and she found it in the end of the first set, so that was the difference".
Sevastova, who retired from tennis in 2013 due to injuries before returning in 2015, withstood a fightback from her 25-year-old opponent late on in the match but sealed the win on her third match point when Stephens sent a backhand into the net.
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Pliskova, the three-time WTA tour ace leader who briefly ascended to world number one previous year, has surprised Williams before at the US Open, beating her to reach her first Grand Slam final in 2016.
After being down 3-1 and facing seven break points, Williams had won eight straight games. She struck three aces in her first two service games and was quickly up two breaks on Pliskova. From there the four-time Olympic gold medalist only continued to gain momentum, her serve once again becoming a reliable threat and her confidence gaining as she began to move to the net and use the whole court. "Doesn't matter that she's No. 17 or 18 now".
"So obviously I know her game really well".
"Serena's one of the best players in the world", Pliskova said after the match. That's just how it is. "That's the most important thing to me".
"It's not what I do out here, but how I can inspire people off the court".
Serena Williams booked her spot in the semi-finals of the US Open with a straight sets win over Karolina Pliskova, although she didn't have it all her own way. "But I don't play dropshots when I see the player struggling or bending over, no", Sevastova told reporters. She's been playing really well for actually a long time. I want to do really well. She clearly knows mine.