On the 21st anniversary of his taking over as manager, Arsene Wenger made nine changes from the side who excelled in the Europa League on Thursday but Arsenal started at the same high-octane level.
After Alexandre Lacazette hit the post in the second minute, they took the lead on 16 when Nacho Monreal struck the ball firmly through a sea of bodies in the Brighton area.
The goal was only the Spaniard’s second in the league — and first for more than four years — and only a fine save from Brighton keeper Matt Ryan prevented Aaron Ramsey doubling their lead just before the interval.
Without the suspended Tomer Hemed, Brighton posed a limited attacking threat and a moment of brilliance from Alexis Sanchez, who backheeled the ball deftly in the penalty area, set up the second for Alex Iwobi on 56 minutes.
“It was a great team play. I didn’t think Alexis would find me but it shows the skill he has,” said Iwobi.
“He is capable of doing anything. To have eyes in the back of his head and backheel to me was amazing.”
Sanchez proved a permanent menace, testing Brighton with his tight turns and inventive passes.
Brighton manager Chris Hughon said: “It was a spirited performance. I can’t accuse the lads of not giving everything. It is always going to be difficult here, levels of concentration have to be for 90 minutes.”