Delray Beach, FL (SportsNetwork.com) - In-form American Donald Young upset Alexandr Dolgopolov at the Delray Beach Open to reach his second semifinal in two weeks.

The left-handed Young, ranked 56th in the world, came from behind to dismiss the fourth-seeded Dolgopolov 2-6, 6-3, 6-4 on the hardcourts at Delray Beach Tennis Center.

Dolgopolov fired 11 aces in a losing effort.

"I thought I fought well," said Young. "I didn't start off the way I wanted to. He was playing pretty well, hitting through the wind and controlling his shots quite good. I decided to buckle down, fight, go out swinging and got a little more not so conservative and it happened to work.

"I feel good. Hopefully it's not over yet ... I'm enjoying it, and I'm going to ride the wave. Hopefully this is not the end and there can be some more."

Young, 25, reached the semifinals in Memphis last week. His opponent Saturday will be capable Australian Bernard Tomic, who defeated qualifier Yoshihito Nishioka 6-3, 6-1 in 57 minutes on Friday.

Also Friday, fourth-seeded Ivo Karlovic topped seventh-seeded American Steve Johnson 6-2, 7-6 (7-4).

The 6-foot-11 Karlovic was the 2010 Delray runner-up. He will face No. 5 seed Adrian Mannarino, who rallied to down Lu Yen-Hsun 3-6, 6-1, 6-1 to reach the semis.

The 2015 Delray champion will earn $84,250.