Tenth seed Gael Monfils defeated Frenchman Lucas Pouille 6-4 6-3 6-3, to become the first man into the semi-finals of the US Open today.Earlier 24th seed Pouille,had three successive five-set wins including the one over 14-times slam winner Rafael Nadal.Monfils, who reached his second career grand slam semi-final and first since 2008 in Roland Garros, will meet either top seed Novak Djokovic or ninth-seeded Jo-Wilfried Tsonga, at Flushing Meadows.