DELRAY BEACH — The ATP has been playing tennis in Delray Beach for a quarter century. In that span, only one top seed has managed to win the tournament, American Mardy Fish back in 2009.

The streak of bad luck for the tournament's top-ranked players continued Wednesday when American Reilly Opelka defeated fellow countryman and defending Delray Beach champion Jack Sock 4-6, 7-5, 6-3. Sock entered the tournament as the highest ranked American on the ATP Tour at N0. 10.

It's definitely great win for me. Jack's a guy I've always looked up to, the No. 1 American," Opelka said after the match. "I have a lot of respect for him. Definitely a big win, big for my confidence. Now I've got to get ready to play the quarter-final."

Opelka said he didn't serve as well as he would have liked during the match but he was pleased with his baseline play. "I thought I hit my forehand great and I made it tough for him to be offense, which is his game."

Opelka will face Peter Gojowczyk of Germany in the quarter finals on Friday. Gojowczyk upset John Isner, the tournament's sixth seed, 7-6 (3), 6-7(4), 7-6(5). Isner, ranked 18th in the world, had a chance to put Gojowczyk away in the third set but the German held on three match points.

"It was a battle," Gojowczyk said. "What a battle! I think both (of us) played well but conditions were tough."

American Steve Johnson beat the ninth seeded Milos Raonic 6-2, 6-4. Raonic was the highest ranked player in the world to compete in Delray, coming a year ago at No. 3. A hamstring injury caused him to withdraw from the tournament just before the finals match with Sock. Injuries plagued Raonic for most of 2017. The rust showed in Raonic's opening match with Taro Daniel, when he had to come back from a 2-5 deficit to take the second match.

Johnson said the win wasn't as easy as it appeared.