Del Potro has looked one of the biggest threats to Nadal's domination this year, with his pulverising forehand dismantling everyone in his path on the Parisian clay. "I just enjoy the fact that I am here again".
The 24-year-old Thiem is now a Grand Slam finalist for the first time, but he has been trending in this direction for a while.
The 29-year-old set up a clash with 10-time champion Rafael Nadal. "Best of five is also a different story".
In truth, however, I'd be mightily surprised if Thiem lost this match.
- Nadal responds to being asked why he still feels pressure on court.
Whether the young Austrian can repeat the feat on the biggest clay court stage of them all come Sunday, however, remains to be seen.
Nadal seldom leaves the door cracked very long. Del Potro, who has struggled with injury, recently, may find it tough to stick with the Spaniard physically and won't have what it takes to knock off the King of Clay.
Although at times during the first set against Del Potro, especially when he was 0-40 down at 1-1 and 15-40 down at 4-4 it looked as though he might be in for a real scrap.
He has dropped just one set so far - at the start of his quarter-final win against Diego Schwartzman - and crushed 2009 US Open champion Del Potro in dominant fashion.
Soon enough, he was yelling at himself, the very picture of exasperation thanks to Nadal's relentless ball-tracking and shotmaking.
His record at Roland Garros now stands at 85 wins and two defeats. Having failed to earned a single break point throughout the set, Nadal pounced when it mattered.
Thiem was in control of his French Open semi-final against the world No 72 Cecchinato, holding three set points in a tie-break for a 2-0 lead.
His decision to enter a smaller tournament in Lyon, France, the week before Roland Garros - an event he won - doesn't appear to have sapped him. The most recent match was in the 2017 US Open, a match Nadal won in four sets.
Nadal has never failed to win the title when reaching the last four at Roland Garros, but knows that Del Potro, who he has lost to five times, is a risky opponent.
Rafael Nadal and Juan Martin Del Potro meet in the semifinals of the 2018 tennis French Open. "I am doing well", he said after edging out third seed Cilic 7-6 (7/5), 5-7, 6-3, 7-5.
The pivotal part of the match was the second-set tiebreaker in which both men played superbly - and both had chances to end it. Thiem went ahead 6-3, but wasted three set points there, including a bad volley into the net at 6-4 that left him chewing ruefully on his left index finger. "He's improving every year". We expect a better Thiem for sure than the one we met a year ago.
"Today, all day, on Philippe Chatrier, the fans said "Forza, Marco", so I think this is the best moment for me", said Cecchinato. "He has the keys, and he has to take advantage".