Rafael Nadal Fails to Make US Open Final After Retiring vs Juan Martin Del Potro

Top-seeded Rafael Nadal retired during his U.S. Open semifinal match Friday, giving No. 3 Juan Martin del Potro his first Grand Slam final berth since 2009. 

Nadal was trailing 6-7 (3), 2-6, when he decided to retire following the second set.

The Spaniard was struggling with his right knee throughout the match and had it examined by the trainer on multiple occasions.

Del Potro was eliminated by Nadal at both the French Open and Wimbledon this year, but Friday's win means he will have an opportunity to win his second career Grand Slam title.

The Argentinian's only other Grand Slam championship win came at the 2009 U.S. Open when he upset Roger Federer.

Nadal seemingly gave everything he had in an opening set that went to a tiebreak, which was largely dominated by del Potro:

It became apparent early in the second set that the knee ailment was hampering Nadal to the point that he couldn't come close to playing his usual style of tennis.

Uche Amako of Express pointed out that Nadal was having trouble chasing down shots, which is usually among his best attributes:

Del Potro broke Nadal early in the second set, and he held what looked to be an insurmountable 4-1 lead based on Nadal's condition.

Per Carole Bouchard of the Yellow Ball Corner, Nadal was visibly upset with the way things were going in the match by that point:

While arguing a call during the second set, Nadal even told the umpire that he planned to retire from the match eventually.

Rafa finally decided to call it quits after losing the second set, which led to a sportsmanlike embrace between him and del Potro at the net:

It can be argued that Friday's result was somewhat fitting considering all the injury issues del Potro has had to overcome since last winning a Grand Slam title in 2009.

This season has been a resurgent one for him, and he is once again among the best tennis players in the world.

His best chance to win a Grand Slam title in nearly a decade will come Sunday when he faces the winner of the other semifinal between Novak Djokovic and Kei Nishikori.