The Czech No.8 seed won her second grand slam singles title this year, but she didn't play any matches after the Paris Olympics.Â
She acknowledged last week not knowing where her level of play was. Turns out, it wasn't good enough.
Krejcikova was no match for Romania's Elena-Gabriela Ruse, who won 6-4 7-5 in New York on Wednesday (Thursday AEST).
"Winning Wimbledon is amazing. It's a great, great, great result, I'm very proud about it and how I was able to handle everything there," said Krejcikova, who hadn't played a tournament on hard courts since February.
"I was playing quite well, definitely better than in the first match. I think my game was improving, but it just wasn't enough."
Ruse got much more work on the US Open's hard courts while playing her way into the main draw through the qualifying tournament and was better than Krejcikova on the points that mattered most.
Elena-Gabriela Ruse, of Romania, has reached the third round of a major for the first time. (AP PHOTO)
She fought back from 5-3 down in the second set to win the final four games.
"Barbora, she's such a good player, she's won so many matches in the last two years and it's just a dream for me," said 26-year-old Ruse.
She advanced to the third round of a slam for the first time and will play No.26 seed Paula Badosa, who eliminated American Taylor Townsend 6-3 7-5.
Badosa continued her strong summer by reaching the third round of the Open for the first time.
Defending champion Coco Gauff cleaned up early mistakes to beat unseeded German Tatjana Maria 6-4 6-0 in a lopsided second-round meeting.
Tatjana Maria (left) and Coco Gauff shake hands after their seocnd-round match. (AP PHOTO)
The American beat Maria in Auckland last year and she held on to the blueprint, roaring back from an error-riddled first set to sweep through the second and close out the affair with a sublime backhand winner.
Former finalist and two-time Australian Open champion Aryna Sabalenka had little trouble beating Italian Lucia Bronzetti 6-3 6-1.
Second-seeded Sabalenka next takes on Ekaterina Alexandrova. The Russian 29th seed ended the run of American 16-year-old Iva Jokic, who suffered from heat exhaustion before losing 4-6 6-4 7-5.
Olympic champion and Australian Open finalist Qinwen Zheng, of China, overcame the loss of the first set to beat Russian Erika Andreeva 6-7 (7-3) 6-1 6-2.
Two-time Australian Open champion Belarusian Victoria Azarenka, who had her blood pressure checked in the second set after calling for the doctor in tears, rallied to beat Frenchwoman Clara Burel 6-1 6-4 to reach the third round.
American 13th seed Emma Navarro swept past Dutch Arantxa Rus 6-1 6-1 to reach the third round for the first time
Germany's Jule Niemeier scored a 6-4 6-0 win over Japan's Moyuka Uchijima to also advance.
- With Agencies
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