Karolina Pliskova and Sofia Kenin, the first and second seeds respectively in the women's draw at the Cincinnati Masters, both suffered defeats in their opening matches on day two of the tournament.
The top eight seeds in the men's and women's draws received first round byes, and on day two of the joint Association of Tennis Professionals (ATP) and Women's Tennis Association (WTA) tournament, being held in New York, some of them were in action as the second round got underway.
Women's top seed Karolina Pliskova of the Czech Republic lost a hard-fought match in straight sets 7-5 6-4 to Russia's Veronika Kudermetova while women's second seed Sofia Kenin also lost in straight sets, as she was defeated 6-1 7-6 by France's Alize Cornet.
First round matches included straight sets wins for 13th seed Anett Kontaveit of Estonia, 6-1 6-3 against Russia's Daria Kasatkina and 14th seed Elise Mertens of Belgium, who comfortably beat Sweden's Rebecca Peterson 6-0 6-2.
In the men's draw, the two top eight seeds in action both enjoyed straight sets victories in their first matches of the tournament.
Greece's Stefanos Tsitsipas, the fourth seed, beat South Africa's Kevin Anderson 6-1 6-3 while David Goffin of Belgium, the seventh seed, beat Borna Coric of Croatia 7-6 6-4 in a closely fought contest.
In first round matches, the ninth seed Diego Schwartzman of Argentina beat Norway's Casper Ruud 7-6 6-3, however it was a different story for the tenth seed Andrey Rublev of Russia who lost 7-5 3-6 6-2 to Britain's Dan Evans.
Karen Khachanov, the Russian, who is seeded 11, beat Alexander Bublik of Kazakhstan 6-4 6-4, while Bulgaria's Grigor Dimitrov, a previous Western & Southern Open champion who is seeded 14th this year, beat Ugo Humbert of France 6-3 6-4.
Matches in this tournament are taking place at the Billie Jean King National Tennis Centre, the same venue that is due to host the year's second Grand Slam, the US Open, which is scheduled to start on August 31.
The Cincinnati Masters, also titled the Western & Southern Open, is an ATP Masters 1000 event and WTA Premier 5 tournament.
Finals in both the men's and women's singles competitions take place on August 28.