Karolina Pliskova acknowledges she's under pressure to perform at the US Open, being No. 1 and having reached the final in 2016.
The Czech has gone three sets in both of the previous two rounds.
"I think I'm playing in quite big waves this tournament so far. So I think sometimes I think I play good shots, good rallies, and then there is hundreds of mistakes and not a good shot," she said.
Pliskova says she's not playing at the same level she was a year ago, partly because of what she did a year ago, defeating Serena Williams in the semifinals and going three sets against Angelique Kerber in the final.
"Never was in this position to defend a final of major. And I'm first seeded, so it's, like, totally different story," she said. "I feel pressure ... I know all the opponents are [ranked] behind me, so I should win every match, which is tough."
Pliskova plays Jennifer Brady, ranked No. 91, in the next round.
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