Defending champion Marin Cilic has claimed that his mental toughness pushed him to victory over Jo-Wilfried Tsonga in their quarter-final clash at the US Open on Tuesday.

The 26-year-old had three match points in the fourth set, but he failed to convert as Tsonga won the tie-break and sent the match into a fifth and final set.

Despite being pegged back, Cilic eventually went a break up in the fifth set before sealing a 6-4 6-4 3-6 6-7(3) 6-4 victory at Flushing Meadows in New York.

After the match, Cilic told reporters: "I didn't play poorly. You know, Jo came up with amazing shots in the critical points, especially on all three match points that I had he played great points.

"I, you know, could have done of course something differently. Could have played some shots differently and pick different spots, but the way I was playing them, I didn't choose any bad shots or that I played bad points.

"Just kept going with it. Sticked with my plan and stayed mentally tough and was very difficult day. Very demanding. Very, very hot, and of course a lot on the line for the match. Obviously with emotions and mentally was very exhausting. So at the fifth set I was, you know, of course feeling a bit tired, but I was able to go through it."

In the semi-finals, Cilic will take on world number one Novak Djokovic following the Serbian's four-set triumph over Feliciano Lopez.