Andree Jeglertz’s side raced to a 3-0 lead within 18 minutes, with an early double from Khadjia Shaw and a first goal for summer signing Niamh Charles.
Brighton, though, rallied before the break with goals from Olivia Garcia and Caitlin Hayes.
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City remain two points ahead of Chelsea, who thrashed Tottenham 6-2.
Lauren James starred for Sonia Bompastor’s side with two goals, which was matched by her team-mate Ellie Carpenter.
Spurs were level at the break thanks to Matilda Vinberg, but three goals in nine blistering second-half minutes swung the game Chelsea’s way.
London City Lionesses made it a full house for the top three, beating Everton 2-1.
First-half goals from Delphine Cascarino and England winger Freya Godfrey had seemingly put the Lionesses in control.
Everton, though, set up a tense finish after substitute Holly McNamara headed in with 20 minutes left.
Manchester United are up to fifth in the table after a third successive league win, seeing off bottom side Charlton 3-1.
Three goals in the opening 13 minutes saw Ella Toone and Andrea Medina put United two up before Leah Davidson pulled one back.
Julia Zigioitti Olme completed the scoring just after the half-hour mark.
Aston Villa stunned faltering Liverpool, coming from behind to secure a 2-1 win for their first league success of the season.
Natalia Ramos scored a spectacular early opener but Villa improved after half-time, with Chasity Grant firing in an equaliser before a Grace Fisk own goal.
Kelly Gago scored the only goal in the first half as West Ham defeated Crystal Palace 1-0.
