Tommy Robredo upsets fifth seeded John Isner while Alexandr Dolgopolov crushed Gilles Simon in the opening rounds of the Valencia Open 500 in Spain on Tuesday.

Both players were hard to break in the first set as they send the set into a tie-break where the 32-year-old Spaniard edged out the American 7-3.

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Robredo was unstoppable in the second set as he converted 91 percent of his serves to pressure Isner and eventually broke the Atlanta Open champion mid-way to win the match 7(7)-6(3) 6-3 in an hour and 21 minutes.

The Shenzhen Open finalist is just three match wins away of his 500^th career victory and now faces Chinese Taipei's Yen-hsun Lu who defeated Guillermo Garcia-Lopez of Spain in two straight sets 6-2 6-3 on Monday.

Another seeded player went down on Tuesday as Ukrainian Dolgopolov shocked eighth seeded Simon in two straight sets with a surprising "bagel" in the first set 6-0 6-3.

The hard-hitting Dolgopolov was spot on with his first serves as he converted 91 percent including five service aces to take down the Shanghai Rolex Masters finalist easily in the first set.

Simon, 29, tried to stage a comeback in the second set as he broke the Ukrainian early but Dolgopolov answered back with two break points to seal the match.

Dolgopolov will now face Jeremy Chardy of France who demolished Tunisian qualifier Malek Jaziri in two sets 6-2 6-1.

Fourth seeded Feliciano Lopez was more fortunate than the two as the Spaniard disposed Slovakian qualifier Norbert Gombos in straight sets 6-4 6-4.

Gombos broke Lopez early in the first set but Lopez came back with a couple of breaks of his own and broke the Slovakian once in the second set to win the match.

Lopez will go up against wild card entry Pablo Carreño Busta in an all-Spanish second round encounter.

Busta defeated fellow compatriot Marcel Granollers who retired while leading 6-2 3-2.

TagsTommy Robredo, Gilles Simon, Feliciano Lopez