"Because if you stay behind the baseline against Dominic, he can take advantage of it", Toni Nadal said.
Leading the tiebreak 6-3, he was powerless as Cecchinato claimed the following four points to earn the first of three set points.
The Italian, who had never won a Grand Slam match before the tournament, faces seventh seed Thiem in the last four.
Cecchinato, who had not won a match in five attempts at a Grand Slam before Roland Garros, fought valiantly against the number seven seed but ultimately the Austrian's star quality shone through to reach his first major final.
Nadal then served out that game. The Spanish ace dropped the first set and was down 3-2 in the second before a rain break swung the momentum in his favour.
Ten-time champion Rafael Nadal reached his 11th French Open final on Friday when he demolished Juan Martin del Potro in straight sets, setting up a title showdown with Dominic Thiem, the only man to defeat him on clay in the last two years.
That was swatted away with Nadal's double-handed backhand, though, and the second set duly went the way of the favourite. 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. "That's the only way for me to approach the tough moments".
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.
Nadal, a 16-time Grand Slam champion, claimed his 85th win here against just two losses after weathering a big-hitting opening from 2009 US Open victor Del Potro to win 6-4, 6-1, 6-2.
"I couldn't play my best because of him", said del Potro, the 2009 U.S. Open champion.More news: Kim Jong Un lands in Singapore, on cusp of making history
"I am sure you will win here in the next couple of years", Nadal told Thiem afterward. That led to 34 winners (eight more than Nadal) but also 42 unforced errors (18 more than Nadal).
Thiem, who beat Nadal in Madrid this season, Rome a year ago and in Buenos Aires on clay in 2016, trails 3-6 in the pair's head-to-head.
The last one in US Open I lost against Rafa.
What went through Nadal's mind right then?
And despite a late stutter as Schwartzman saved three match points, Nadal wrapped up victory to keep alive his hopes of equalling Margaret Court's record of winning a single Grand Slam singles title 11 times. "But all my semi-finals in Grand Slams were against them".
Nadal is looking as comfortable as ever on the Philippe Chatrier court where has previously won the title 10 times. "When (Thiem) is dominating the point, he is very unsafe".
Del Potro had required treatment on a hip problem suffered early in the first set and he visibly wilted in the second, raising his arms in mock celebration when he won a solitary game while already 5-0 behind.
The Argentine has never beaten Nadal on clay.
The 16th-seeded Gauff, who is 14 years old, beat 15th-seeded Leylah Annie Fernandez of Canada 6-4, 6-3.
"That", del Potro would say later, "was my chance".