The only thing standing in the way of the first U.S. Open showdown between Roger Federer and Rafael Nadal was Juan Martin del Potro.
Stand in the way he did.
The 24th-seeded del Potro shocked the third-seeded Federer in Wednesday's quarterfinal match at Arthur Ashe Stadium in Flushing, New York, 7-5, 3-6, 7-6(8), 6-4.
Del Potro is now two victories away from a U.S. Open title, but another tournament in New York passing by without Federer and Nadal facing each other remained a curiosity considering they have 37 head-to-head meetings, 12 of which occurred at Grand Slams.
ATP Media Info highlighted how close U.S. Open fans have come to the matches:
Federer was uncharacteristically off at times Wednesday. The five-time U.S. Open champion committed 41 unforced errors and won 73 percent of his first-service points compared to 81 percent for the victor, per the tournament's official website.
"I knew going into the match that I wasn't in a safe place - I Knew I wasn't good enough in my mind or my game," Federer said, per David Law of BBC Radio 5.
With Federer struggling, Del Potro seized control of the match in a tense third-set tiebreak that extended to 10-8:
Fellow Argentine Manu Ginobili was firmly on del Potro's side by that point:
Despite the loss, Federer enjoyed a 16-5 advantage in head-to-head meetings entering Wednesday's match. However, del Potro prevailed in the final of the 2009 U.S. Open—arguably their most famous match—and prevented the 19-time major winner from enacting revenge at the same venue in this year's quarterfinal.
Del Potro wasted little time establishing himself and earned the first break of the match before parlaying it into a 7-5 set victory by holding serve.
He was particularly effective with the forehand in the opening set, which he unleashed on the final point:
Federer quickly fought back, notching a critical break in the second to go up 3-1 and finishing the rest of the set on serve without much challenge. Momentum was fleeting for the five-time U.S. Open champion, though, as del Potro broke on a double-fault in Federer's first service game of the third set.
The Swiss star broke back to force a tiebreak but couldn't take advantage of multiple set points, dropping it 10-8.
Matt Zemek of Patreon summarized Federer's up-and-down showing:
Things only got worse for the 19-time major winner in the early stages of the fourth set when del Potro broke to move ahead 3-2 after Federer missed a clear smash shot at deuce.
With the break in hand, del Potro continued to control the pace with his serve and clinched the victory. It was more impressive play from him on the major stage considering he was coming off an emotional five-set comeback against No. 6 seed Dominic Thiem in which he won a combined three games in the first two sets and trailed 5-2 in the fourth before prevailing.
He will look to continue his elevated play in Friday's semifinal against Nadal.
Nadal holds an 8-5 advantage in head-to-head meetings, although del Potro won the last two. He will need to replicate and even build on his Wednesday performance if he wants to stretch his winning streak against the tournament's top seed to three.