New Haven, CT -- (Sports Network) - Top-seeded Fernando Verdasco of Spain and last year's runner-up Mardy Fish were quarterfinal winners Thursday at the $708,000 Pilot Pen Tennis event, a final U.S. Open tune-up.

Verdasco held off German Mischa Zverev 6-2, 7-6 (7-4), while an eighth-seeded Fish handled lucky-loser and fellow American Jesse Levine 6-3, 7-6 (7-4) on the hardcourts at the Connecticut Tennis Center. Verdasco and Fish will do battle here in Friday's semifinals.

Fish was last year's New Haven runner-up to fellow American James Blake.

A day-five upset came when Slovenian qualifier Luka Gregorc overcame seventh- seeded Italian Andreas Seppi 4-6, 6-4, 7-5. The world No. 434 Gregorc, who upended second-seeded Croat Ivo Karlovic here on Wednesday and ousted 14th- seeded Argentine Jose Acasuso on Tuesday, will now appear in his first-ever ATP semifinal.

He will be joined by Croatia's Marin Cilic, who also caught the upset train with a 6-3, 6-2 victory over fourth-seeded Igor Andreev.