The 22-time Grand Slam champion, who missed most of the 2023 season, is aiming to compete at Roland Garros in May, where he has triumphed a record 14 times.
“On a personal level, for what is to come, the 6-1 in the second set is what had to happen today,” said Nadal, who explained there were bigger challenges ahead.
Nadal said the key to being able to triumph at Roland Garros was continuing to build in the weeks ahead.
“(I need to be) getting the weeks of experience, of matches, and feeling more comfortable with everything,” continued Nadal.
“Today I felt more comfortable than yesterday … I have to be realistic, today I cannot have a game that goes for two and a half hours, or three.”
Nadal, a 12-time champion at the Barcelona clay-court tournament, cruised past Flavio Cobolli in his first ATP Tour match since January. However, his journey was halted by Alex de Minaur, who has now secured victories in their last two encounters.
Despite showcasing glimpses of his unparalleled skill on the court named after him, Nadal succumbed to defeat in what he described as “realistically” his final appearance at the tournament.
De Minaur seized an early break in the first game and applied pressure with a series of exquisite drop shots, leaving Nadal struggling to retrieve them.
Although Nadal fought back with a break of his own, taking a 4-3 lead, De Minaur responded by breaking to love and clinching the first set 6-5.
The momentum shifted in favour of the 25-year-old Australian, who dominated the second set by breaking Nadal three times and ultimately sealing victory as Nadal’s shot went long.
“I’m sad because nobody wants Rafa to stop playing,” said De Minaur.
“I never thought I’d get a win over Rafa on clay, it’s something I’ll be able to say when I finish my career.”
Earlier Norway’s three-time Grand Slam finalist Casper Ruud came out on top in an entertaining 6-3, 6-4 match with Alexandre Muller to reach the third round.