Djokovic, Federer face tough tests to making finals

Novak Djokovic of Serbia hits the ball to Feliciano Lopez of Spain during their quarterfinal match at the U.S. Open Championships tennis tournament in New York, September 8, 2015. REUTERS/Carlo Allegri

NEW YORK (Reuters) - Novak Djokovic and Roger Federer remain on course for a marquee one-two clash in the men's U.S. Open final, but each must first vanquish a formidable opponent and friend in Friday's semi-finals at Flushing Meadows.

World number one and top seed Djokovic, seeking to finish a brilliant season with a third grand slam triumph, will try to end the reign of 2014 champion Marin Cilic of Croatia in the opening men's semi-final.