Clinging to his lifeboat serve, which regularly reached 137 miles per hour, John Isner was able to take young Briton Kyle Edmund to a fourth-set tiebreaker in their third-round U.S. Open match Friday night. But no farther.

Edmund, a 21-year-old ranked 84th in the world who upset No. 13 Richard Gasquet of France in the first round, held off No. 20 Isner, 6-4, 3-6, 6-2, 7-6 (5), to set up a fourth-round match with defending champion Novak Djokovic.

Isner, who leaves the tournament with a huge lead in aces with 100, struck 27 in the match — 11 of those in the last set as he was dangling over the abyss. Serving at 5-6 in the fourth, Isner pounded three consecutive aces to necessitate the tiebreaker.

He hit two more in the tiebreaker to keep the score at 3-3. But, from there, Isner’s inability to lift a backhand half-volley over the net gave Edmund a minibreak. Isner then lifted a lob long, followed by an Edmund forehand that caught less than an inch of the baseline to give him a triple match point at 6-3.

Isner’s inside-out forehand saved the first of those, and his service winner saved a second. But Edmund ripped a forehand to the open court to end the two-hour, 43-minute duel.

“Playing John,” Edmund said, “your chances don’t come often, so you have to catch those when they come. With his serve, when you get a racket on the ball, just try to keep it in the court.”

Edmund spoke several times during the first week of how, “In my head, I am thinking, ‘You’re creating good pressure here. Just keep patient . . .’ In my head, I am thinking, ‘It will come. Just don’t panic.’ ” He didn’t.

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Earlier, Ryan Harrison, a 24-year-old qualifier based in Austin, Texas, playing in the third round for the first time, was beaten by veteran Cypriot Marcos Baghdatis, 6-3, 7-6 (4), 1-6, 6-1. In the second set, Harrison led, 5-3, before stumbling to the tiebreak.