Jan-Lennard Struff spoiled Denis Shapovalov's 20th birthday by posting a 5-7, 6-3, 6-1 victory on Monday in the first round of the Monte Carlo Masters at Monaco.
Shapovalov was plagued by 51 unforced errors against just 22 winners.
His reward is a second-round meeting with Grigor Dimitrov, who defeated Matteo Berrettini on Sunday.
Russian 10th seed Daniil Medvedev advanced easily over Portugal's Joao Sousa 6-1, 6-1, but Hungarian Marton Fucsovics dumped out Nikolaz Basilashvili, the 12th seed, 7-5, 3-6, 6-1.
British No 1 Kyle Edmund suffered a disappointing 4-6 6-3 6-1 defeat by Diego Schwartzmann to start his clay court campaign in underwhelming fashion.
The 24-year-old won only one of the final 13 games against Schwartzman, who is one place below him in the world rankings.
The highest-seeded victor on Monday was No. 10 Daniil Medvedev, who needed just 55 minutes to trounce Portugal's Joao Sousa 6-1, 6-1.
"It was a good match".
The first set in the match saw five breaks of serve before the Brit had a chance to serve out the set and he snatched it on his first set point. "You want to see how your practices have been going [and if] they worked out". Cecchinato will face Switzerland's Stan Wawrinka in the second round.
Fabio Fognini survived an early scare in his first round match with qualifier Andrey Rublev which ended 4-6 7-5 6-4. Fognini faced a 1-4 deficit in the second set before storming back to win in two hours, 30 minutes.
Belgium world No.21 David Goffin moved to the second round with a comfortable 6-1 6-4 win over Guido Andreozzi on a day when most of the other main names also made it through unscathed. Goffin had five aces while winning in 85 minutes.
Djokovic, champion at this event in 2013 and 2015, will take on Philipp Kohlschreiber after the German cruised past Taro Daniel 6-1, 6-3.
Kohlschreiber next faces top-seeded Novak Djokovic. The match will be Nadal's first in over a month after he injured his knee at Indian Wells in March.