Now ranked 30th in the world, the loss is another early exit for the Canadian this season. Auger-Aliassime, a former world No 6, now drops to 6-6 for the year with his latest defeat.
Cobolli, ranked No 69, will face the winner of the match between Russian Roman Safiullin and Greek Stefanos Tsitsipas, the No 5 seed, next.
This was the second top 30 win for Cobolli in his career.
Acapulco ATP 500, other first-round matches (Princess Mundo Imperial Resort, hard, USD 2,206,080):
- Alex De Minaur (3) beat Taro Daniel: 6-2, 6-1
- Yoshihito Nishioka (LL) beat Nuno Borges: 3-6, 6-2, 6-4
- Sebastian Ofner beat Ernesto Escobedo (WC): 6-7 (7), 6-4, 7-6 (4)
- Ben Shelton beat Daniel Evans: 2-6, 7-5, 7-6 (5)
- Jack Draper beat Tommy Paul (7): 6-0, 6-4
- Miomir Kecmanovic beat Diego Schwartzman (WC): 4-6, 6-3, 6-1
- Rodrigo Pacheco Mendez vs. Dusan Lajovic
- Alexander Zverev vs. Daniel Altmaier
- Michael Mmoh vs. Holger Rune
- Aleksandar Kovacevic vs. Jordan Thompson
- Casper Ruud vs. Christopher Eubanks
- Terence Atmane vs. Dominik Koepfer
- Frances Tiafoe vs. Max Purcell
- Roman Safiullin vs. Stefanos Tsitsipas
- Matteo Arnaldi vs. Taylor Fritz
