Second-ranked defending champion Coco Gauff crashed out in her opening match at the WTA and ATP Cincinnati Open, falling to Kazakhstan's Yulia Putintseva 6-4, 2-6, 6-4 on Thursday.

The second-round shock to America's Paris Olympic flag-bearer stunned a partisan crowd in the US heartland in the final major tuneup for the US Open on August 26, where Gauff is defending champion.

Putintseva, ranked 34th, has made a recent habit of upsets, knocking off world number one Iga Swiatek in the Wimbledon third round barely a month ago.

"I'm really proud of myself," said Putintseva. "Even if the crowd was cheering for Coco, they were fair with me. "These courts are so fast, you have to just play on instinct. That's what I did."

Gauff became the youngest winner at Cincinnati a year ago at age 19 and carried that success into her first Grand Slam triumph at the US Open.

Putintseva will next face Spain's Paula Badosa, who defeated Anna Kalinsyaka 6-3, 6-2. (AFP)