Giovanni Simeone and Riccardo Sottil were on target for Vincenzo Montella's Fiorentina in the 2019 ICC curtain-raiser at SeatGeek Stadium.
Scores were level at half-time after Simeone cancelled out Javier Lopez's 25th-minute opener and Guadalajara's Alan Pulido failed to convert a penalty.
But Sottil secured victory for Fiorentina – which ended last season without a win in its final 14 Serie A matches – courtesy of a great solo goal in the 52nd minute.
Italy star Federico Chiesa started on the bench amid growing links with Juventus, while midfielder Jordan Veretout was absent ahead of his reported move to Roma.
It was a lively start by both teams, with Fiorentina's Simeone and Guadalajara's Isaac Brizuela going very close inside the opening 11 minutes.
Guadalajara broke the deadlock against the run of play thanks to Lopez, whose seemingly harmless long-range strike wrongfooting goalkeeper Bartlomiej Dragowski following a deflection.
The Mexican side's lead was short-lived, however, as Simeone's glancing header restored parity for Fiorentina two minutes later and Diego Simeone's son almost put Viola ahead after forcing Jose Rodriguez into a fine save.
Guadalajara had a golden opportunity to restore their advantage 10 minutes before half-time after a contentious handball on Aleksa Terzic, but Alan Pulido's awful penalty was easily saved by Dragowski.
Fiorentina took the lead seven minutes into the second half thanks to a fabulous piece of skill from Sottil, who turned his opponent and curled a shot past Rodriguez after the Guadalajara keeper had denied Marco Benassi from close range.
Dusan Vlahovic came off the bench to replace Simeone and rattled the crossbar with a ferocious effort in the 69th minute as the match finished with a host of substitutions.