Roger Federer has saved two match points and come back from two sets to love down, to beat Gael Monfils and advance to the US Open semis for the ninth time.

Federer struggled in the first two sets in the windy conditions, and Monfils took full advantage.

But the five time former champion refused to give in and gradually turned the tables on the Frenchman to post a dramatic victory 4-6, 3-6, 6-4, 7-5, 6-2.

Federer next takes on Croatian Marin Cilic.