Rafael Nadal is into yet another French Open final.
"For sure", said Thiem's coach, Gunter Bresnik, "this gives you a little hope".
But at 4-5 Thiem's serve let him down badly, handing Nadal three set points.
Cecchinato had never won a grand slam match until the French Open.
Cecchinato, who up until this year's Roland Garros never got past the first round of a Grand Slam event, did not look the same in the third set, as he hit just one victor, committing eight unforced errors.
Just like that, Nadal was off on a five-game burst to lead 3-0 in the second set.
And the first set was indeed tight, even with del Potro calling for the trainer at 2-3.
Nadal certainly lived up to his "King of Clay" nickname in Friday's semifinal against Juan Martin del Potro, crushing the sentimental favorite 6-4 6-1 6-2 to reach a record 11th final at Roland Garros.
"He's a big favourite against everybody", Thiem said. The world No. 1 became the second man in the Open Era to make 11 finals at the same major, tying friendly rival Roger Federer's mark on the grass of the All England Club.
"I have lost a lot of opportunities through injuries, and I know the years are going quick".
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Nadal, by contrast, had not had a sniff on Del Potro's serve until, at 5-4, two swishes of his forehand forced two set points, the second of which he converted when the Argentinian netted.
"Today‚ all day‚ on Philippe Chatrier‚ the fans said "Forza‚ Marco"‚ so I think this is the best moment for me‚" said Cecchinato.
"When asked why he still felt stress before resuming on Thursday despite all of his past achievements, Nadal said: "(Because) I am a human person.
The No. 1-ranked Nadal compiled a 35-20 edge in winners while making only 19 unforced errors Friday.
Nadal tightened his grip, going to 5-1 on another double break in the third set and sealed the match when Del Potro hit a backhand long.World 72 Cecchinato had knocked out three seeded players to reach the semi-finals, including 12-time major victor Novak Djokovic in the quarter-finals.But Thiem, 24, was too strong and now believes he has a particularly powerful weapon on his side for the final - breakfast. "But all my semi-finals in Grand Slams were against them".
Thiem‚ who was playing in his third successive French Open semi-final‚ admitted the second set had been a nervy encounter after needing five set points to get through it.
Thiem will be out of his comfort zone again when he goes into battle with Nadal in his maiden grand slam decider on Sunday.
Nadal will retain the world number one ranking if he wins - but that will be the last thing on his mind. Thiem withstood a barrage of break points to hold in a marathon sixth game, which he thought he had won at 40-30 when he left a wide ball, only for the umpire to overrule the line judge. Nadal had more trouble with another Argentine, the diminutive Diego Schwartzman, in the quarterfinals.
The forecast says there is a chance of rain.