Gael Monfils wins on 40th birthday at US Open

NEW YORK — Gael Monfils stood in the middle of the court and bowed to the crowd that was treating the Frenchman to a roaring ovation on his 40th birthday. The match was still a ways from ending. But after leaping in the air to smash a forehand winner — a daredevil shot that few outside one of tennis’ ultimate showmen might even attempt — there was no reason to wait. Monfils turned back the clock and pushed back the end of his Grand Slam career, beating Adolfo Daniel Vallejo 2-6, 6-1, 6-2, 6-0 on Tuesday night at the US…