Delray Beach: US second seed John Isner rallied Friday to reach the ATP Delray Beach Open semi-finals, where he will try to deny Marin Cilic his third final in as many weeks.

Big-serving Isner fired 18 aces in outlasting US qualifier Rhyne Williams 4-6, 6-3, 6-2 while Cilic, a seventh seed from Croatia, dispatched Russia's Teymuraz Gabashvili 6-2, 6-3.

Cilic won his fourth career ATP crown on home soil at Zagreb two weeks ago and last week reached the Rotterdam final, losing to Czech Tomas Berdych.

Hitting 12 aces and converting five of six break points, Cilic advanced in 79 minutes and took the 2014 lead in match wins with 16.