Karlovic, 35, beats 18-year-old Kokkinakis at Delray Beach

DELRAY BEACH, Fla. (AP) Ivo Karlovic beat an opponent close to half his age, outlasting teen Thanasi Kokkinakis in two tiebreakers in the second round of the Delray Beach Open.

Karlovic, who turns 36 at the end of the month, showed no signs of age in defeating the 18-year-old Kokkinakis 7-6 (7-4), 7-6 (7-2) on Wednesday.

With a serve that more than once topped 135 mph, Karlovic advanced against the qualifier from Australia who won his first ATP main draw match earlier this week.

The fourth-seeded Karlovic, a runner-up here in 2010, moved into the quarterfinals, where he will face seventh-seeded Steve Johnson or 17-year-old Russian Andrey Rublev. Also advancing was fifth-seeded Adrian Mannarino of France, who needed less than an hour to dispatch Denis Kudla, a 22-year-old American, 6-2, 6-2.