David Ferrer stunned by Stanislas Wawrinka in Cincinnati

Stanislas Wawrinka has caused a minor upset at the Cincinnati Open by knocking out fourth seed David Ferrer in straight sets.

In a tight opening set the Swiss found an elusive break of serve to go 5-4 ahead, but Ferrer then failed to convert two break points as Wawrinka edged him out 6-4.

Spaniard Ferrer had little go his way in the second, with the world number 22 easing past him 6-1.

Wawrinka's victory has set up a third-round encounter with Kei Nishikori following the 14th seed's victory over James Blake.