On a sunny Easter Sunday, it was Brighton who started on the front foot, Jelena Cankovic with an audacious effort from range which forced Daphne Van Domeselaar to tip the ball over the bar after just 60 seconds.
The Seagulls caused more issues from the following corner, with Arsenal having to clear two efforts from Charlie Rule off the line n a matter of seconds.
In a first half of very few opportunities, it was Smilla Holmberg who had the best chance from point blank range. Chiamaka Nnadozie somehow getting her foot to the ball, and preventing it from rustling in the bottom corner.
Having dealt with all sorts of pressure in the first half, Brighton took the lead just three minutes half-time interval, Madison Haley latching onto Fran Kirby's through ball and smashing her effort into the top left corner.
The Seagulls continued to put Arsenal under pressure, and Van Domeselaar was needed to prevent Carla Camacho from making it 2-0.
Arsenal were shellshocked once more when Caitlin Hayes header hit the top corner, the visitors were two goals up, but thoroughly deserved that lead for how they had played in the opening period of the second half.
The Gunners were really struggling to deal with the Brighton pressure, and nearly went 3 goals down as Kirby slid in, and was unable to connect with the fizzling ball that had gone right across the six yard box.
Arsenal had to throw everything at the final 10 minutes, Nnadozie got down to her left hand side to deny a powerful strike from Laia Codina.
Alessia Russo's effort from close range flying over the crossbar summed up the frustration for Renee Slegers side, they were dominant in possession, though unable to break down the low block that Brighton were in, only three shots on target from 13 shots reflected that.
Katie McCabe went close with a free kick flying just wide of the top right corner in the final moments of added time, and while they had been very sloppy in the final third, Brighton had stuck to the game-plan and were now one game from the FA Cup Final.