Roger Federer rallies from 5 sets down to beat Serena Williams in New York . Monfils held two match points on Croatian Marin Cilic 's serve at two -4 in the fourth set . Wozniacki plays China 's Peng Shuai . The Swiss next meets resurgent Croatian Marin Cilic in the semifinals . Serena Williams plays Roger Federer in the women 's semifinals Friday .
Roger Federer rallies from 5 sets down to beat Serena Williams in New York . Monfils held two match points on Croatian Marin Cilic 's serve at two -4 in the fourth set . The Swiss next meets resurgent Croatian Marin Cilic in the semifinals . Serena Williams plays Roger Federer in the women 's semifinals Friday .