Rafael Nadal was relieved to punch his ticket to the Madrid Open quarter-finals after a tough first set against American Sam Querrey.

The underdog seemed to have Nadal on the ropes and was one point away from a 5-1 lead in the first set before the Spaniard fought back to prevail 6-4 6-2. It was Nadal's 12th-straight match win and the fifth seed attributed his slow start to playing at night for the first time in the tournament.

"I hadn't trained during the night time, it was a completely different feeling," Nadal said. "Today it was a little bit slower. At the beginning, when we were warming up, I was feeling a little bit strange, but actually during the week I've been training well and playing well."

"After [the slow start] I just had to come back and turn the match around. Luckily once I did that, the match went well. It was on my side most of the time."

"He was going to serve for 5-3 with new balls. You know that you're at the limit and you can lose the set. Not the match, because you still have another set to go, but it is tough [to be in that position]. In that moment I decided to step back a little bit and change my game. I tried to close the gap so that he couldn't just go for it. I think it worked out."

Nadal will now take on Portugal's Joao Sousa, who is playing his first ATP 1000 quarter-final after beating Jack Sock.