Brighton shocked Watford at Vicarage Road with a 3-0 result.
Abdoulaye Doucoure put the Hornets on the back foot through an own goal, accidentally poking a Montonya’s cross past Ben Foster.
The hosts looked to respond right away but Doucoure could not make amends as he blasted over from range. They continued to mount pressure at Brighton’s goal but without finding a breakthrough.
Javi Gracia wasted no time to act as he summoned Roberto Pererya from the bench to replace Deulofeu at half-time.
Watford started to force issues and won a free-kick just outside the Brighton box in the 56th minute.
Pereyra stepped up but could only hit the wall before he yelled at referee Craig Pawson for a penalty as the Argentine claimed there was a handball somewhere. The referee checked with VAR and no penalty was awarded.
But it is Brighton’s substitutes that make the difference as Florin Andone, who replaced Jurgen Locadia on minute 64, extended their lead by getting on the end of a Davy Propper cross before making a first-time finish past Ben Foster.
Then new signing Neal Maupay made an immediate impact on his debut after he came on for Glenn Murray.
Lewis Dunk made an exquisite throughball that took about six Watford players out of the game to find Maupay in a dangerous area, and the striker jinked past Foster and rolled the ball into the net.
It was an impressive opening day for Brighton, who face West Ham at the Amex on Saturday. Watford, meanwhile, take on Everton at Goodison Park the same day.