John Isner has battled past American compatriot Jared Donaldson to earn his place in the last 16 at Queen's.
The 30-year-old fired down 21 aces to secure a 7-6 6-4 victory over the teenager, who had come through the qualifying rounds at the weekend.
Despite 140 places separating the two players in the world rankings, Donaldson held his own during a 68-minute first set, but he couldn't come through a tie-break and that turned out to be the pivotal point of the match.
The teenager stayed with Isner during the opening stages of the second, but the world number 18 eventually recorded the break that would almost inevitably secure him the contest.
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