Top-seeded John Isner barely avoided an upset Thursday night in the Atlanta Open, outlasting 19-year-old wild-card entry Christian Harrison 7-6 (9), 4-6, 7-5 to reach the quarterfinals.
Harrison, ranked 373rd in the world, fought off three match points before the 22nd-ranked Isner closed it out with the last two of his 29 aces.
Isner will play James Blake on Friday. Blake beat eighth-seed Evgeny Donskoy 6-3, 6-2.
Harrison broke Isner's booming service game just once, but it came at a critical time as Isner double-faulted to give Harrison the second set point. Isner broke Harrison only once as well, to take a 6-5 lead in the third when Harrison's forehand return from the baseline found the net.
Earlier, Christian's brother, 21-year-old Ryan Harrison beat fourth-seed Igor Sijsling 6-4, 6-3 after trailing 1-4 in the first set.