Petra Kvitova says she was trying to emulate Serena Williams as she survived two match points before winning a thrilling final-set tie-break to beat ninth seed Garbine Muguruza.
The Czech won 5-7 6-3 7-6 (12-10) to reach the last 16 of the US Open.
"With Serena last night it was amazing how she was saving those match points and I was trying to do the same," the two-time Wimbledon champion said.
Williams saved five match points before losing to Ajla Tomljanovic on Friday.
Kvitova came from 5-2 down in the third set, saving two match points with Muguruza 6-5 ahead in the decider.
In the tie-break, Spaniard Muguruza then saved three match points before 21st seed Kvitova came through in New York.
She will face eighth seed Jessica Pegula after the American beat Yuan Yue of China 6-2 6-7 (6-8) 6-0.
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