Top seed Isner advances at ATP Delray Beach

Isner, who is looking to regain his form after battling a knee injury earlier this year, on Tuesday got off to a slow start against Canada's Levine but played an efficient third set to win 7-6 (7/3), 5-7, 6-4.

"I knew it was going to be a tough match," Isner said. "The first match outdoors is always tough.

"Very different conditions. Jesse's good. I've always had trouble with him," he added.

"Honestly, it was a good one to get through. A win is a win and I haven't had many lately. I'm just trying to get this train going. I'll rest up and I anticipate I'll be better."

Isner reached the semi-finals in Delray Beach last year. He moves on to play Japan's Go Soeda, who survived a third-set tie-break to defeat last year's finalist Marinko Matosevic.

Soeda trailed 3-6 in the tie-break but managed to save three straight match points during a five-point winning streak to claim the match 2-6, 6-4, 7-6 (8/6).

Former winner Kei Nishikori retired in the first set Tuesday with an oblique strain when trailing hard-serving Ivo Karlovic 4-5.

The Japanese No. 1 Nishikori was fresh off winning his third career ATP Tour title Sunday in Memphis.

Fourth seeded Nishikori beat American James Blake in the Delray Beach final five years ago for his first career ATP Tour title.

His improved six spots in the world rankings to No. 16 after his win on Sunday.