WASHINGTON — Jannik Sinner became the first teenager to win an ATP 500 event, beating Mackie McDonald 7-5, 4-6, 7-5 to take the Citi Open title Sunday.

Sinner, who turns 20 on Aug. 16, won his third ATP title and second this year. He was the first Italian finalist in this tournament's 52-year history, and he became the event's third-youngest champion, behind 18-year-old Andy Roddick in 2001 and 19-year-old Juan Martin del Potro in 2008.

Teenagers had been 0-5 in ATP 500 finals since the category was created in 2009.

McDonald, a 26-year-old American playing in his first ATP final, made the fifth-seeded Sinner work. The second set was the first that Sinner dropped in this tournament, and after the Italian went up a break early in the third, McDonald battled back.

Sinner failed to convert two match points while up 5-2, and McDonald fought all the way back to 5-all before eventually falling short. Sinner broke McDonald's serve again to end the match, winning it when McDonald's backhand went into the net on the final point.

Although Sinner took the first set, McDonald set the tone for the match by fighting off 10 set points. Six of those came with Sinner up 5-4, and the other four were at 6-5. McDonald had his serve broken three times in the set, and Sinner had his broken twice.

In the doubles final earlier, Raven Klaasen of South Africa and Ben McLachlan of Japan beat Neal Skupski of Britain and Michael Venus of New Zealand 7-6 (4), 6-4.

AP