Home favourite Mikhail Youzhny bowed out of the St Petersburg Open in the second round as Guillermo Garcia-Lopez held his nerve to go through.
The Spaniard had to survive a fightback by the second-seeded Russian before triumphing 6-4 4-6 6-3 to book his place in the last eight.
Denis Istomin, seeded eight, joined him despite losing the first set to Andrey Golubev, fighting back to win 4-6 6-3 6-4.
But earlier, third seed Janko Tipsarevic failed to repeat his Davis Cup heroics as he succumbed in the first round.
The man who clinched Serbia's place in the final with victory over Canada over the weekend, went down 7-6 (4) 6-3 to Spaniard Roberto Bautista Agut.
Agut saved eight of the nine break points he faced to win in an hour and 50 minutes.
There was an early exit too for fifth seed Fernando Verdasco, who lost 6-3 6-4 to Ukrainian world No 92 Sergiy Stakhovsky.
However, sixth seed Ernests Gulbis took just 41 minutes to book his place in the second round with a 6-0 6-1 rout of wild card entry Mikhail Elgin.
There were first-round victories too for seventh seed Lukas Rosol, Konstantin Kravchuk, Joao Sousa and Michal Przysiezny.