A pair of second-half goals and a performance high on endeavour, effort and organisation saw them through in relative comfort.
The result ranks alongside a 2-1 win at Chelsea in the WSL five years ago among the greatest in the club’s history.
Madison Haley opened the scoring on 48 minutes with a brilliant finish and Caitlin Hayes added a towering header from a corner 15 minutes later.
Fran Kirby created both chances and her clever forward play always asked the Gunners questions.
The win also owed much to a half-time tactical switch by head coach Dario Vidosic after he had been disappointed to see his side’s bright start fade as they struggled with a bobbly pitch.
Albion created all the early danger.
Jelena Cankovic had a searing drive from outside the box tipped over by the leaping Daphne van Domselaar.
From the corner, Haley’s header and Charlie Rule’s shot were both blocked right in front of goal.
Arsenal were generally well contained but they should have gone ahead just after the half-hour.
Chiamaka Nnadozie made a superb point-blank block from Smilla Holmberg but the Arsenal player should have scored from Chloe Kelly’s excellent cross.
Albion sent on Carla Camacho for Kiko Seike at the break and adjusted their shape.
The breakthrough came soon after – and in spectacular style.
Haley took down a long ball and played a one-two with Kirby.
The return pass seemed to be sending Haley a touch wide but she stretched and whipped a sensational finish high across the startled van Domselaar.
Arsenal were clearly going to respond and Holmberg sent an effort across the face of goal.
But there was nothing else of note and they lost Beth Mead to injury after a tussle with Manuela Vanegas.
Albion doubled their lead from a corner on 63 minutes as Hayes soared at the far post to head home a Kirby corner from outside the six-yard box.
Brighton and Hove Albion's Caitlin Hayes celebrates scoring their side's second goal of the game during the Adobe Women's FA Cup, quarter-final match at the Mangata Developments Stadium, Borehamwood. Picture date: Sunday April 5, 2026. PA Photo. Photo credit should read: Steven Paston/PA Wire. RESTRICTIONS: Use subject to restrictions. Editorial use only, no commercial use without prior consent from rights holder.Caitlin Hayes celebrates her goal (Image: Steven Paston/PA Wire)
Arsenal sent on Alessia Russo and upped the tempo in a bid to retrieve the tie.
But Kirby might have added a third herself when she was inches from touching home a low cross delivered by Camacho.
The former England star then chipped over after picking off a loose pass.
Nnadozie dived to her right to parry a shot from Laia Codina in a late Arsenal flurry and home fans were encouraged by the announcement of eight minutes of stoppage time.
But Albion held firm.
Albion: Nnadozie; Minami, Hayes, Vanegas; Rule, Symonds, Cankovic, Olislagers (Mpome 81); Seike (Camacho 46), Kirby (Noordam 81), Haley (McLauchlan 89).