Thirteenth-seeded Alexandr Dolgopolov became the first upset at the Western & Southern Open, losing to 50th-ranked Nikolay Davydenko 6-1, 6-1 in the first round on Monday.
Davydenko, ranked as high as No. 3 on the tour in 2006 and 2007, needed just 52 minutes to beat Dolgopolov, who was won the Citi Open in Washington on Aug. 5.
Dolgopolov, a Ukrainian ranked 16th in the world, committed 26 unforced errors to just three by his Russian opponent.
Twelfth-seeded Marin Cilic of Croatia survived a challenge from qualifier Sergiy Stakhovsky before advancing with a 6-3, 4-6, 6-4 win.
In other men's matches on the tournament's first full day, Andreas Seppi of Italy beat the Netherlands' Robin Hasse 6-4, 6-4; qualifier Jesse Levine beat Donald Young 6-4, 7-6 (2) in a matchup of Americans; Taiwan's Yen-Hsun Lu eliminated Poland's Lukasz Kubot 6-3, 6-0; and American wild-card Brian Baker outlasted Philipp Kohlschreiber of Germany 7-6 (7), 7-6 (4).
Stanislas Wawrinka of Switzerland needed three sets to get by French qualifier Paul-Henri Mathieu 6-2, 3-6, 6-1. And Lleyton Hewitt advanced with a 6-4, 6-4 win over Russian Mikhail Youzhny
Serbian Victor Troicki beat Croatian qualifier Ivan Dodig 6-4, 7-5, Spain's Pablo Andujar cruised past Australian qualifier Marinko Matosevic 6-4, 6-3, German Florian Mayer defeated qualifier Fabio Fognini of Italy 7-5, 6-2, and Uzbekistan's Denis Istomin eliminated France's Julien Benneteau 6-3, 6-1
The women's tournament got underway with a mild upset as Peng Shuai won a grueling three-setter over 13th seeded Jelena Jankovic 5-7, 7-5, 7-6 (8).
Jankovic, last year's runner-up and the 2009 champion, lost at love while serving for the match in the second set, including a double-fault at 0-40, and blew a total of five match points against her Chinese opponent.
The 66th-ranked Timea Babos, a 19-year-old Hungarian, knocked out 39th-ranked Varvara Lepchenko of the United States 7-6 (4), 6-4. Babos lost in the final round of qualifying on Sunday but reached the main draw when Ana Ivanovic withdrew because of a toe injury.
Eleventh-seeded Dominika Cibulkova of Slovakia earned a routine 6-3, 6-4 win over qualifier Akgul Amanmuradova of Uzbekistan.
Italy's Mona Barthel beat Spain's Maria Jose Martinez Sanchez 6-0, 6-4; Anabel Medina Garrigues of Spain defeated Romanian Simona Halep 6-3, 6-0; Germany's Julia Goerges won in straight sets over Israel's Shahar Peer 6-3, 6-3; and Sweden's Johanna Larsson beat Australia's Casey Dellacqua 6-1, 6-3.
Also, wild card Camila Giorgi eased past fellow Italian Francesca Schiavone 6-1, 6-3; and Eleni Daniilidou of Greece outlasted Vania King of the United States 6-3, 2-6, 7-6 (6) in a matchup of qualifiers. Another qualifier, Urszula Radwanska of Poland, advanced with a 6-2, 6-4 win over Ksenia Pervak of Kazakhstan
Olympic singles champion Serena Williams is the women's tournament favorite and will begin Tuesday in her campaign to win the Cincinnati title for the first time.