"We've always had tough matches,'' Fish said. "We've had three-setter most every time if not every time. I think I've figured out what to do.''
Fish is 4-1 against Spadea, and all their previous meetings went the full three sets. Fish, who reached the final in 2003, is hoping to become the first top seed in the 17 year history of this tournament to score the winner's trophy.
"It's fun to be the marked guy and everybody is gunning for you,'' said Fish, who reached the final in San Jose, Calif., earlier this month.
Spadea, who reached at least the quarters here every year since 2004, has been fighting a virus and fever since playing his first-round match, was his first tour-level victory since Los Angeles in August.
"I think there are some factors, and those factors being that he's improved, he's playing well and I was under-conditioned,'' Spadea said. "I just didn't have a lot of energy out there and my whole game thrives on energy, and grinding, and getting an extra ball back, and winning ugly, really.''
Fish will play sixth-seeded Florent Serra, who outlasted Mischa Zverev 6-3, 4-6, 6-4.
Serra, who was behind 0-3 in the third set, won the match with an exquisite crosscourt drop volley from his heels.
"It's very important for me to be in the quarterfinal,'' Serra said. "I need to serve better tomorrow because he serves very good and my return is OK, but I need to focus on my own service percentage.''
Seventh-seeded Jeremy Chardy will play Andrey Golubev and former Australian Open finalist Marcos Baghdatis faces Dudi Sela to determine the two remaining quarterfinalists.
The two other quarterfinal pairings were decided on Wednesday - qualifier Evgeny Korolev will face Guillermo Garcia-Lopez and 2000 Delray Beach champion Stefan Koubek squares off against Christophe Rochus.
Fish bests Spadea to advance at Delray Beach
Valencia Always Go Out To Win - Unai Emery
