Tiafoe grinds down Dimitrov to set up all-American semi-final at US Open

• Bulgarian retires while trailing 6-4, 6-7 (5), 6-3, 4-1
• World No 20 faces Taylor Fritz next with for spot in final

An American will play in the US Open men's singles final for the first time in nearly two decades after Frances Tiafoe held off Grigor Dimitrov to reach the last four at Flushing Meadows on Tuesday night, setting the stage for an all-American semi-final with Taylor Fritz.

Seizing on a weary opponent and feeding off a rowdy Arthur Ashe Stadium crowd squarely in his corner, Tiafoe ran out to a 6-4, 6-7 (5), 6-3, 4-1 lead before Dimitrov retired from their quarter-final with an injury shortly before midnight. Tiafoe advances to the semi-finals for a second time in three years where he will face the No 12 seed Fritz, a long time friend and Davis Cup teammate, who sprang a 7-6 (2), 3-6, 6-4, 7-6 (3) upset of the No 4 seed Alexander Zverev during the daytime session.