Lee Geum-min secured a shock win for Brighton as Women's Super League title hopefuls Manchester City suffered back-to-back defeats.
City have already dropped eight points from their first six games with their bid to win the division suffering early setbacks.
Lee combined with fellow former City player Pauline Bremer to bundle past Khiara Keating at the far post in the 81st minute.
The hosts were on top throughout and had 35 shots, hitting the woodwork twice, but failed to make the most of their dominance and were made to pay.
Manchester City had never before lost to Brighton, and had only once failed to win in their eight previous meetings.
Brighton goalkeeper Sophie Baggaley repeatedly kept her side in the game as they held on before snatching a late victory.
Their chances were limited, only hitting the target on three occasions, before securing an unlikely smash-and-grab win.
It was Brighton's second unexpected result in as many weeks after holding Manchester United to a 2-2 draw last time out.
City were beaten away at Arsenal last weekend.
Early title setback as City stunned
Manchester City's bid for the WSL title seems to already be unravelling.
Chelsea lost just two games as they won the division last season - City have already lost as many times in their first six games.
The hosts - who finished 11 points behind Chelsea last season - dominated possession and had the better of the chances but the Seagulls dug deep to stop City finding any way to dent the scoreline.
Gareth Taylor's side showed promise going forwards and Chloe Kelly hit the woodwork after just 20 seconds.
England forward Kelly looked most likely to find a path to victory but couldn't get the better of Baggaley's determined performance, and the Brighton defence limited City's clear-cut chances.
Khadija Shaw and Mary Fowler had good chances denied while Lauren Hemp toiled but hit the crossbar amid the search for a late leveller.
The home side could not find their clinical edge on a frustrating afternoon, with their 13 shots on target unable to create the breakthrough.
And there will be no respite for Taylor's side as they take on neighbours Manchester United in the derby at Old Trafford next weekend.
Historic success for Brighton
Brighton finished just five points clear of relegation last season - now they've triumphed over one of the favourites to win the WSL.
They might not have had much control over proceedings but that won't be what they remember about this fixture.
Baggaley's services, managing 13 saves, undoubtedly kept the Seagulls in the game and created the platform for their dramatic win.
There were other rare moments of positivity for Brighton, particularly through Elisabeth Terland's attacking efforts in the first half, but they spent nearly all the game on the back foot.
They achieved just 16 points across the entirety of last season but they already have seven after just six games this time around.
Melissa Phillips has managed to steer her side to four points from games against Chelsea, Manchester United and Manchester City, and they'll need to be on top form again next weekend when they host Arsenal.