The 37-year-old Croat outlasted Luxembourg's Gilles Muller 6-7(2) 7-6(5) 7-6(12) to win the grasscourt Hall of Fame Championships in Newport, Rhode Island -- becoming the oldest champion in the tournament's history.
In saving three match points before downing Muller, the big-serving Karlovic became the oldest Tour winner since Marty Riessen (37 years, nine months) in Lafayette in 1979.
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It was his third consecutive Newport final, having lost the previous two. Karlovic now has seven career titles, the first coming in 2009.
"After all these years when I was losing in the final and now I was finally able to do it," world number 35 Karlovic said. "And I was down a match point. That makes it even nicer."
Karlovic, who returned from a left knee injury earlier this year, became the oldest man to reach the third round of a grand slam for 25 years at this year's French Open, eventually losing to runner-up Andy Murray.
At Roland Garros, 51 men aged 30-plus began in the main singles draw -- a new grand slam record -- while there were 49 30 somethings in round one at Wimbledon.
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