Pliskova, who had been a match point down in her previous match, destroyed Jennifer Brady 6-1 6-0 in just 46 minutes to move into the US Open quarter finals.
She admitted: "I think I'm playing in quite big waves this tournament so far...
I think one of the best, even this year", said Pliskova after reaching her second straight US Open quarterfinal. The Czech Republic native is in the quarters for the second consecutive year. "The thing I'm most impressed by is her determination to play one point at a time".
Brady's usually strong serve betrayed her - she put only 16 of 41 first serves in play - and she hit only six winners, to 23 for Pliskova.
It was Safarova who got off to the best start in the tiebreak, securing a mini-break in the opening point, though quickly lost it as Vandeweghe began to sense victory.
If she will match last year's result at Flushing Meadows, Pliskova will keep the world No. 1 seat next Monday when the ranking will be updated.
Nadal turned in his most powerful performance yet at this year's NY tournament to beat Dolgopolov on Monday (NZT Tuesday), and is now just one win away from a potential semifinal showdown with longtime rival Roger Federer.
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Pliskova said: "Today I was much better".
"We both have the plan to play aggressive, but I think she's a little bit, not messy sometimes, but she's just going for her shots".
Yesh: Kanepi has had the most under-the-radar dream run at a Slam that I can remember.
This time, she raced to a 4-0 lead against an obviously nervous opponent, then won the second set in even more lopsided fashion.
For the first time since 2002, half of the women's quarterfinalists at the U.S. Open are Americans.
"It's my fourth match on this court and I enjoyed playing here as always". "My energy dropped. Once I got broken in the third, I just kept telling myself: 'Just try to figure it out". I was lucky that I had an wonderful crowd and atmosphere. Sloane Stephens will mark her third, and Vandeweghe her fourth. No U.S. Open women's quarterfinals have featured three Americans since 2004, and no men's quarterfinals had featured any Americans since 2011. It may be that I have given him the opportunity to play well, said Brady.
Pliskova joined countrywoman Petra Kvitova in the last eight, following Kvitova's win over Wimbledon champion Garbine Muguruza. Del Potro had won his only major title in his career and had put an end to a series of five titles, Federer in NY.