That he trailed by a set and a break before rain delays allowed him to change tactics and recover to get there?
"Of course, I didn't expect to be in the top five again, to reach the semifinals at the big tournament after all my injuries", del Potro said.
Both men advanced by winning quarterfinals suspended the night before because of rain.
The pair were locked at 5-5 in a first-set tie break when the rain came, and it was fifth seed Del Potro who took the first two points upon the resumption to draw first blood. "Maybe the day when you can beat Rafa was yesterday".
Del Potro fought back tears during his post-match interview and was loudly cheered by fans at Court Suzanne Lenglen.
In dropping the opener on Wednesday, Nadal had lost a set at Roland Garros for the first time since a 2015 quarter-final defeat by Novak Djokovic.
It will be Halep's second consecutive Grand Slam final after she lost the title match at the Australian Open in January.
"It has been a long time without a good feeling in my body. I don't have words to explain what this means to me and my team".
"It was someone who made a loud [sound] before my serve, and I made [a] double fault", Del Potro said. This year, he has a chance to stop Rafael Nadal, who seems en route to his 11th title here. So I have nothing to lose tomorrow. In Wimbledon, I lost against [Novak] Djokovic.
"I am living all my career with that", Nadal said after fending off another Argentine, the feisty, relentless Diego Schwartzman, in four sets, 4-6, 6-3, 6-2, 6-2 on Thursday.
Nadal struck 34 winners and Schwartzman racked up 64 unforced errors as the "King of Clay" joined Bjorn Borg and Roger Federer in becoming the only men to reach 11 semifinals in the same major in the Open Era.
Juan Martin Del Potro is coming off a four sets win over Marin Čilić that took 40 games to decide.
When they return to the stadium, Nadal will be serving at 5-3, 30-15 in the second set.
Nadal's serve was picked apart by Schwartzman on Wednesday, but the world number one conceded just one point from his first three service games.
And Nadal knows he will be in for a hard afternoon where defensive play is not an option. I knew it was going to be a tough match and I was a little bit more nervous than usual.
His problems began in 2010 when a wrist injury kept him out for much of the year, and despite returning to prominence, and reaching a Wimbledon semi-final in 2013, they re-materialised - nearly costing Del Potro his career.