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.
Once Nadal stole the opener with a break in the 10th game, it was one-way traffic as he left Del Potro trailing in a cloud of Parisian clay dust to set up a final against Dominic Thiem.
"But I'm also aware that here it's tougher", said Thiem, the first Austrian in a major final since Thomas Muster won in Paris in 1995.
In his on-court speech after Nadal's 6-4, 6-3, 6-2 victory, the 24-year-old Thiem said: "I still remember when you won here the first time, 2005".
The win continues Nadal's undefeated run on championship weekend in Roland Garros - the Spaniard has never lost in Paris after reaching the semifinals.
"I know I have to play my best, I have to improve a little bit".
"But I believe I will be ready for the final."World number one Nadal went into Friday's clash with a 9-5 career record against Del Potro, including all three meetings on clay.However, it was Del Potro who was in the ascendancy in the rallies in the first set. So I need more work for go top 10 or top 20, so these matches was very important for me". He pounded huge serves that topped 135 miles per hour (220 kph) - about 25 miles per hour (40 kph) better than Nadal's fastest - and translated into seven aces but also had five double-faults.
Del Potro's play this tournament, plus his history against Nadal - the fifth seed won two of their three previous duels and was the last foe to down the Mallorcan in a grand slam semifinal in 2009 - suggested a close tilt.
Thiem has shown in the past that there is a way to beat Nadal on a clay court by simply hitting every ball as hard as he can.
Cecchinato, whose career was nearly derailed two years ago by a match-fixing scandal before his name was cleared, stopped the rot in the sixth game.More news: Putin: We are Ready to Meet Trump as Soon as Washington is
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When del Potro avoided a bagel in the sixth game of the second, he raised his arms in celebration.
Over the past two seasons, Nadal is 49-2 on red clay, with both losses coming against Thiem: in the quarterfinals at Rome in May 2017, and the quarterfinals at Madrid in May 2018. He impressively recovered from a slow start to make the first set close.
Thiem led 6-3 but suddenly lost focus.
One of those victories came against Thiem in last year's semi-final and was, if anything, more comprehensive than this one.
Rattled by the Italian's revival, Thiem clicked into overdrive - and aided by Cecchinato unforced errors - clinched a crucial break for 6-5 by crunching a forehand victor.
"I can not believe it now", Karin Thiem, a tennis coach, told a group of reporters.
"If I'm facing Rafa, I'm not the one who has the pressure", he said.
"I was lucky or - lucky or I don't know what to say for them".
The smile never left her face.
He concluded, however, by saying: "It's not easy". So when I had the chances, I just tried to convert. The diminutive shot maker halted Nadal's record of straight sets.