WASHINGTON — Gael Monfils won his first title in 2 1/2 years, erasing a match point and breaking Ivo Karlovic twice in the span of four service games Sunday during a 5-7, 7-6 (6), 6-4 victory in the Citi Open final.

Monfils, a Frenchman seeded No. 2, prevented the 37-year-old Karlovic from becoming the oldest man since 1973 to win ATP singles tournaments in consecutive weeks.

And Monfils did it by figuring out a way to just barely neutralize the big serve of the 6-foot-11 Karlovic enough to matter.

Up until 5-4 in the second set, when Karlovic served for the championship, the 13th-seeded Croatian had won all 53 of his service games in the hard-court tournament.

But Monfils came through there, converting his seventh break point of the match when Karlovic pushed a forehand volley long. Karlovic put his hands on his hips, knowing he’d come so close to ending things right then and there.

Karlovic then was a single point from victory at 6-5 in the ensuing tiebreaker, but a 116 mph serve by Monfils produced a backhand return that sailed long. A couple of points later, Monfils owned that set, and he broke again to lead 2-1 in the third.

Soon enough, Monfils ended Karlovic’s eight-match winning streak, which included a title last week on grass at Newport, Rhode Island.

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Not since 43 years ago, when Ken Rosewall won back-to-back events a month shy of his 39th birthday, has a man older than Karlovic won two ATP titles in a row.

But instead of that feat, it was Monfils who managed to give himself a rare victory in a final.

He entered Sunday having lost 19 of 24 career finals, and 8 of his last 9. Monfils earned $348,200 in prize money for his first title since February 2014 at Montpellier, France, and the most important of his career — his first at an ATP 500 tournament, which refers to how many ranking points the champion collects.

Karlovic’s intimidating serve can take over a match, especially on speedy surfaces such as grass or hard courts. With the temperature nearing 100 degrees Sunday, it made for even tougher conditions for Monfils to try to deal with those high-bouncing serves.

Monfils, who is 29, tried a bit of everything.

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At the outset, he stood way back to return, to no avail, dropping 18 of the first 19 points Karlovic served (the lone exception was a double-fault).

Occasionally, Monfils would shuffle back and forth behind the baseline while awaiting serves.

And later, he moved much closer to the baseline while receiving, a tactic that seemed to help.

Daniel Nestor and Edouard Roger-Vasselin won the men’s doubles title, beating Lukasz Kobot and Alexander Peya 7-6 (3), 7-6 (4).