Cecchinato mixed it up with drop shots and gradually found his range to set up three break points at 4-3, which Thiem saved thanks to his strong first serve.
Top-ranked Simona Halep has rallied past Angelique Kerber 6-7 (2), 6-3, 6-2 to reach the French Open semifinals.
Austrian Dominic Thiem faces arguably the biggest challenge in sport, overcoming Rafael Nadal on the Court Philippe Chatrier clay, if he is to join the Grand Slam winners' club on Sunday.
But this year's final is already different from any of Nadal's previous 10 in Paris or any of his 13 other Grand Slam finals.
"I think it helps, definitely, knowing that you were the last guy to beat him", said Bresnik, whose association with Thiem spans more than 15 years. "I have a plan", a confident Thiem, who dispatched surprise package Marco Cecchinato 7-5 7-6 (10) 6-1 in the semi-finals on Friday, told reporters.
Nadal goes past Borg's record of six titles and ends Djokovic's bid to be the first man since Rod Laver in 1969 to hold all four majors. "I just try to keep that going". As odd as it seems, Thiem played one match against Thomas Muster, who won the title here in 1995 when in his pomp. If he wins the game, OK.
"He's an awesome player", Nadal said. But I'm also aware that here it's tougher.
So nerves could come into play in the early going against Nadal, who will be bidding for his 17th major title overall.
Rafael Nadal has dropped a set at the French Open for the first time since 2015.
Relentless Nadal broke to love at the start of the third, and as he moved on to match point an exhausted Del Potro paused for breath, bent double, as if he had been punched in the stomach.
"I played again one of my best matches on clay", Halep said after coming back from a break down in the second set. I'm not interested in these things, I just play tennis.
There was cause for concern, also, when Nadal quit with a leg injury in the fifth set of his quarter-final against Marin Cilic at the Australian Open this year, heightened when he then withdrew from hard-court tournaments in Acapulco, Indian Wells and Miami - but he has blossomed on the red dirt of Europe.
The Argentine was a break down in the third but turned it around as the errors started to creep in for Cilic, who was bidding to reach the last four for the first time here after falling in the quarter-finals a year ago.
Nadal had not even dropped a set in the tournament since that match against Djokovic, a run of 37 in a row that ended in the opener against the 5-foot-7 (1.70-meter) Schwartzman, an Argentine eyeing his first appearance in a major semifinal.
Federer, who has skipped the French Open, has reached 11 Wimbledon finals, winning eight.
For 24-year-old Thiem the odds are firmly against him beating clay-court king Nadal, but the Austrian says the pressure will not all be on him on Sunday.
In 2016, Cecchinato was accused of match-fixing and suspended for 18 months, but he appealed, and his punishment was dropped on a technicality.
In the second-set tiebreaker Friday, Thiem went ahead 6-3, but missed out on three set points there, including a bad volley into the net at 6-4 that left him chewing ruefully on his left index finger.