Venus Williams, fresh off a stirring run to last week's Montreal final, ran out of gas in Cincinnati as she fell 6-7 (2) 6-3 6-4 to 16th seeded Czech Lucie Safarova in first-round action at the Western and Southern Open on Tuesday.
Williams, who beat her top-ranked younger sister Serena to reach the Rogers Cup final where she fell to Poland's Agnieszka Radwanska, looked ready to make another run in Cincinnati after taking the opening set in a tiebreak.
But the seven-times grand slam champion could not manage to convert any of four break chances in the second while Safarova converted her one and only opportunity to level the match.
Safarova, a Wimbledon semifinalist, stepped up the pressure in the third with two more breaks to clinch her first win in five career meetings against the 34-year-old American.
"It was definitely a quick turnaround, maybe would have been a little better to play a little later in the day," said Williams, back in top 20 for first time since March 2013 following her runner-up finish at Montreal.
"But she just played so well. No matter what shot I hit she hit a winner, or if I hit it really deep she somehow managed to control it down the line."
Spanish 15th seed Carla Suarez Navarro, an upset winner over Maria Sharapova in Montreal, was also made to work for her spot in the second round needing three-sets to tame Bulgarian Tsvetana Pironkova 6-3 1-6 6-2.
(Reporting by Steve Keating in Toronto; Editing by Frank Pingue)