After defeating Rafael Nadal, Lucas Pouille believes an increased mental strength has aided his impressive run to the US Open quarter-finals.

Before 2016 the Frenchman had never been past the second round at a grand slam, and Sunday's epic five-set win over Nadal means he has reached the last eight at two successive majors and will climb into the ATP top 20 at the end of the tournament.

Pouille had gone the distance against Marco Chiudinelli and Roberto Bautista Agut in each of the previous rounds and although Nadal had cruised through without dropping a set, it was the 24th seed that advanced to a quarter-final meeting with compatriot Gael Monfils.

The 22-year-old recovered from 4-2 down in the deciding set before retaining his composure having given up a 6-3 lead in the tie-break, and believes he is physically and mentally stronger than ever.

"I moved to Dubai. We work a different way. We work, I think, harder," he said.

"During the pre-season I changed many things. I took my own physical trainer. He's travelling almost every time with us so we can work every day. Even in tournaments we keep working. We keep working.

"I think mentally I'm stronger. I took a lot of confidence.

"The way I'm going on court is not the same as last year. I think that's why I'm better than the year before. Of course, I'm a bit older, as well."

However, Pouille said it was too early to say whether the breakthrough victory would change his career.

"No, it could maybe. I will tell you in few months or in few years," he said." Now if I say, yeah, of course it's going to change my career and in one year I am [ranked] 50 I will be wrong.

"Maybe it will change my career, but I will see. It will give me a lot of confidence for the next round, for the rest of the season. But now I have one more match to play again, so we'll see after the tournament."