Spanish superstar Rafael Nadal has admitted that "he didn't play well enough" against Lucas Pouille in the fourth round of the US Open on Sunday, which saw him lose 6-1, 2-6, 6-4, 3-6, 7-6 in what is the biggest upset of the tournament so far.

In arguably the most exciting match of the tournament so far, a tie-break was needed to separate the two players, with the 22-year-old Pouille keeping his composure to win the biggest match of his career with a brilliant forehand that Nadal could not chase down.

"Today the attitude was great. In terms of energy, in terms of motivation, I was great. In terms of tennis I needed more. I needed to serve better in some moments. I needed to create more pain on the opponent with my shots. That was something that I didn't make today. He played well, I didn't play bad but I didn't play well enough", as quoted by ATPWorldtour.

This loss snaps a brilliant 12-year run for Nadal who has made the quarter final of every Grand Slam he has played in. Since his first French Open title in 2005, the Spaniard has made a total of 20 Grand Slam finals, advancing to at least quarterfinals every year since 2006.

Rafael Nadal
This is the first time in 12 years that Rafael Nadal has not made the quarter-final of a Grand Slam Getty

However, the 14-time Grand Slam winner has confirmed that this loss will not deter him going ahead in the future and that he still has more tennis in him.

"Losing in the fourth round after having a big chance to play a great event here, feeling myself ready for it, for sure I am not very satisfied, no? I am sad. But that's it, I give it my best, I try my best. I fight until the last ball, I need to improve in other things, but I am going to do it", the Spaniard added further.

Lucas Pouille, who is ranked number 25 in the world, will meet fellow countryman Gael Mofils in the quarter-final.