New York - Rafael Nadal tackles Juan Martin del Potro on Friday for a place in the US Open final, wary of the Argentine giant whose game he describes as having the power to leave opponents "dead."
World No 1 Nadal, the 2010 and 2013 champion, enjoys a 8-5 career edge over 2009 winner Del Potro, who knocked out Roger Federer in the quarter-finals.
The 31-year-old Spaniard is 22-3 in Grand Slam semi-finals, winning the last 14 in which he has appeared.
However, his last loss at this stage came on the same New York hard courts in 2009 at the hands of Del Potro, who went on to shock Federer in the final, ending the Swiss legend's five-year reign.
"Juan Martin is a top player. When he's playing well, it's difficult to stop him," admitted Nadal, who has lost his last two meetings on hardcourts with the 28-year-old.
"I have to play my best tennis," Nadal said. "If you let him play from good positions with his forehand, you are dead, because he plays super-aggressive, hitting so hard."
While French Open champion Nadal looks to take another step closer to a 23rd Grand Slam final and 16th title at the majors, Del Potro is making up for lost time.
Playing in his first semi-final at the Slams since losing the longest ever last-four clash to Novak Djokovic at Wimbledon in 2013, Del Potro is riding a tidal wave of emotion in New York.
Unable to prosper fully from his 2009 US Open breakthrough, he was just 20 when long-term struggles with wrist problems began, requiring four surgeries and pushing him to the brink of retirement.
Del Potro has been virtually running on empty. He had to save two match points and come back from two sets down to beat sixth seed Dominic Thiem in the last 16.
He almost retired from that titanic clash, suffering from breathing difficulties and a fever.
But he said the passionate support of Argentine fans, many dressed in the light blue football shirts of their country, kept him going.
Of the four semi-finalists - South Africa's Kevin Anderson and Pablo Carreno Busta feature in the other match - Del Potro is the only player to have faced three top-20 seeds.
As a result, the former world number four is match-tough even if he doubts he has the stamina to last the distance against Nadal, who took just 97 minutes to see off Russian teenager Andrey Rublev, losing just five games.
"Personally, I like to play against him when I'm in good condition. But it's not the case at this moment," said Del Potro.
"He's also a lefty, so he has chance to find easily my backhand.
The mouthwatering clash between Nadal and Del Potro has overshadowed the match-up between 28th-seeded Anderson and Carreno Busta, the 12th seed from Spain.
Both are playing in their first semi-finals at the Slams.
They have thrived in a half of the draw missing Andy Murray, who pulled out on the eve of the tournament, while the absence of Djokovic and 2016 champion Stan Wawrinka further changed the complexion of the title chase.
Anderson has a 2-0 career edge, including a win last month in Montreal, over Carreno Busta, who has reached the semi-finals helped by facing four qualifiers.
The 31-year-old Anderson is bidding to become the first South African in the US Open final since Cliff Drysdale in 1965.
"We are so used to the same guys being there, and they have had such unbelievable consistency," said Anderson, Florida-based but born in Johannesburg.
"To see a couple of them in the other half, a couple of them unable to play this year, it gave some of the guys an opportunity."