Locked in a tight test at the U.S. Open, Rafael Nadal conjured up an over-the-shoulder, back-to-the-net flick of a volley victor that he celebrated with a leap and punch of the air.
That familiar problem returned on break point in the first game of the fourth set, giving Nadal a crucial break which he doubled for a 4-0 lead after seeing off a break point. Schwartzman was absolutely relentless in his attempt to win the point, and his lunging forehand passing shot could end up being one of the best shots of the entire tournament. He won the first game of the set before Cilic won the second game.
"That shows what a great year I'm having, that the work I've been doing is paying off".
It was an agonising defeat for 33-year-old Monfils, the last French representative at this year's major, and added to his NY woe five years ago when he squandered two match points at the same stage to Swiss star Roger Federer.
Nadal's path to the final sees him take on Schwartzman next after the 5ft 7in (1.70m) Argentine chopped down sixth seed Zverev. After losing the second set, Nadal cruised into the quarterfinals by winning the final two sets 6-2, 6-1.
Reflecting on his win, Nadal was quoted by the Association for Tennis Professionals (ATP) as saying,"It's easy to describe, but hard to make".
"It means a lot to me to have him supporting".
Yet the momentum was suddenly dragged away from him by some remarkable returning from Nadal in an exhilarating fourth game of the third set.
On Friday, Nadal will play Matteo Berrettini.
Tennis great Roger Federer has won practically every trophy available in his outstanding career thus far but after crashing out of the US Open quarter-finals the Swiss is unsure if he'll win a record-extending 21st Grand Slam.
Diego Schwartzman matched his best Grand Slam showing by reaching the quarter-finals. That match gave me confidence. Schwartzman had won only two sets in the previous 17 against Nadal.
On Friday, Nadal will play No. 24 Matteo Berrettini, a 23-year-old from Rome who is Italy's first male semifinalist in NY since 1977.
"I think it is a huge honour, playing in front of this crowd, but also playing in front of Tiger is very special", he said.
"I'm going to take the positive from these two weeks", he added.
"The past six, seven months have been pretty rough for me". But Schwartzman never went away, making an awesome series of gets at 15-0, finally shoveling a forehand victor down the line before raising both arms to get the crowd involved.In the moment, it seemed like Schwartzman was simply enjoying his time in the world's biggest tennis stadium. "I'm happy to get a bit of a break now, go back to practice, reassess and attack from there".