The referee blows the whistle, and the visitors see off the late Arsenal rally to secure the three points as they run out 2-1 victors.
They took the lead on 28 minutes when Mwepu laid the ball off to Trossard before the forward placed the ball into the top corner.
The hosts thought they were level just before the break as Martinelli headed home from a corner.
However, the Brazilian was offside as Gabriel nodded the ball back to him.
The Seagulls doubled their lead in 66 minutes when Mwepu turned from provider to scorer.
As he fired home a brilliant first-time effort after Caicedo found him on the edge of the box.
The hosts got back into it late on, as they hit the post twice in a couple of seconds.
Before an Odegaard shot from a distance deflected off Welbeck and over Sanchez into the back of the net.
Arteta’s men came streaming forward as they searched for a late equaliser, but a brilliant Sanchez saves and a Cucurella clearance off the line denied them and was enough for Brighton as they saw the game out to collect all three points.
ARSENAL (4-3-3): Aaron Ramsdale; Cedric Soares, Ben White, Gabriel, Granit Xhaka; Martin Odegaard, Albert Sambi Lokonga, Emile Smith Rowe; Bukayo Saka, Alexandre Lacazette, Gabriel Martinelli.
BRIGHTON AND HOVE ALBION (3-5-2): Robert Sanchez; Joel Veltman, Lewis Dunk, Marc Cucurella; Enock Mwepu, Pascal Gross, Moises Caicedo, Yves Bissouma, Alexis Mac Allister; Leandro Trossard, Danny Welbeck.
Brighton, take the lead!!! It’s a brilliant team goal that puts them in front, as a clever move ends with Mwepu rolling the ball back to Trossard in the middle of the box. The Belgian shoots the first time and places it perfectly into the top corner to make it 1-0 to the visitors.
What a goal!!! The Seagulls double their lead with a sublime finish from Mwepu. Caicedo digs the ball back from the byline to his teammate on the edge of the box, and the Zambian midfielder fires first time into the bottom corner to make it 2-0.
The hosts are back in it!!! Odegaard shoots from miles out, and it takes a big deflection off Welbeck and loops over Sanchez to make it 2-1 Arsenal.
So, what’s next?
Those three points on their travels mean that Brighton moves up to 11th place, level on points with ninth-placed Crystal Palace.
They face a test away at Tottenham next time out as they look for a solid finish to the season.
The win here will give them hope of getting a good result at the Tottenham Hotspur Stadium.
Defeat for the hosts means they’ve lost three of their last four league matches and miss the opportunity to move into the top four.
They will travel to Southampton in their next match and reignite their assault on the Champions League spots.