Nikolay Davydenko's 6-4, 4-6, 6-3 defeat of fifth-seeded Frenchman Gilles Simon was the biggest shock of the first round matches in the Valencia Open 500 on Monday.
Davydenko's win broke a five-match losing run for the Russian against Simon, currently number 12 in the ATP Rankings, and hits the Frenchman's hopes of reaching the ATP World Tour finals in London next month.
Simon was the first big name to be knocked out here.
Davydenko will next meet Simon's compatriot Nicolas Mahut who beat Spaniard Guillermo Garcia-Lopez 7-6 (7-5), 6-2 in the last 16.
Another shock on Monday was Canadian qualifier Vasek Pospisil's win against John Isner of the US, clinching a third set tie-break 11-9.
After the twenty-one year old Pospisil, currently ranked 133 in the ATP rankings, took the first set 6-3, the big American, ranked 110 places higher, returned the gesture by the same score to set up the tight third set.
Pospisil now faces a match in the last 16 against the winner of Tuesday's all-star Spanish duel between number one seed David Ferrer and Fernando Verdasco.
The Italian Fabio Fognini comfortably beat Spaniard Daniel Gimeno-Traver 6-4, 6-3 and will face the winner of Tuesday's clash between fourth seed Nicolas Almagro and Argentine Juan Monaco in the last 16.
Monaco did play on Monday in the Men's Doubles event with partner Juan Ignacio Chela, his Argentine Davis Cup partner.
The pair were beaten, however, by Spaniards Marcelo Granollers and Marc Lopez 6-4, 7-6 (6-2), in a result that does not bode well for their possible participation in the Davis Cup Final to be played between Spain and Argentina on December 2-4.