Geummin Lee scored the only goal nine minutes from time as Albion stunned Manchester City to claim their second win of the WSL season.
Head coach Melissa Phillips wanted her team to build on last week’s encouraging 2-2 draw against Manchester United and they produced a superb defensive display.
Phillips' side only had 34% possession and six shots to the hosts' 35 but former City player and substitute Lee swept home Pauline Bremer’s inch-perfect cross nine minutes from time to secure our first win over City at the tenth attempt and end City’s 21-match unbeaten home run.
Albion nearly fell behind after 18 seconds when Chloe Kelly's 20-yard strike rattled the crossbar and then the England international stung the hands of Sophie Baggaley from just inside the box.
The visitors responded well to this early onslaught, however, as City goalkeeper Khiara Keating did well to block Elisabeth Terland's goalbound volley following a lovely floated cross from Katie Robinson.
Tatiana Pinto was the next to test Keating from 12 yards after Brighton's high press, which was causing City problems early on, turned the ball over in the home team's final third.
Conversely, the hosts looked dangerous down the right wing and should have taken the lead when an unmarked Jill Roord failed to bury Kelly's cross into the six-yard box.
Kelly and Filippa Angeldal were then denied by Baggaley - who was player of the match against United last weekend - shortly before the break, as a strong defensive rearguard kept the hosts at bay.
Gareth Taylor's side were inches away from breaking the deadlock just after the interval but Khadija Shaw couldn't keep her close-range header under the bar following potent wing play from Lauren Hemp.
Guro Bergsvand, who scored a rare goal last time out, was at her defensive best to make a last-ditch challenge to stop Kelly from finding the back of the net.
It seemed it would not be City's day when Lionesses star Hemp found the side netting from a yard out after Kelly's whipped delivery across the face of the goal, and then Roord fired straight at Baggaley deep inside the area.
The former United goalkeeper got down well to her right to keep out Hemp's swept effort from nestling into the corner and then substitute Kerstin Casparij miscued with the goal gaping.
Then, against the run of play, ex-City forward Bremer drove into the box and her pass across the six-yard box was tapped in by Lee in the 81st minute.
The hosts hit the bar again through Hemp but try as they might, they could not find a way through against an indomitable Albion side.
The priceless three points saw Albion rise to eighth in the table, whereas City, who previously averaged four goals a game against the Sussex side in the WSL, dropped to fifth with their second straight defeat.
Albion: Baggaley, Li Mengwen (Rule 78), Bergsvand, Thorisdottir, Kullberg, Losada (Symonds 63), Pinto (Carabali 46), Zigiotti, Robinson (Sarri 96), Bremer, Terland (Lee 63)
Unused subs: Evrard, Pattinson, Hawkesby, Startup