Brighton's Kiko Seike scored in the fifth minute of stoppage time to deny promoted Birmingham City their first win back in the Women's Super League.
On a pulsating afternoon at St Andrew's, the WSL 2 champions established a two-goal lead through Oceane Hurtre and Lily Crosthwaite and held on grimly in the face intense Albion pressure.
Olivia Garcia pulled a goal back late to give new Brighton boss Arturo Ruiz hope before Seike wriggled clear in the final seconds to fire a deserved equaliser.
Birmingham had won plaudits for their performance and attacking endeavour at champions Manchester City on opening day, only to lose 3-1 at Joie Stadium.
Boss Amy Merricks had promised they will continue to stick to their attacking principles and would have been delighted with the clinical finishing of Hurtre and WSL 2 player of the season Crosthwaite.
It was far from one-way traffic though, with Fran Kirby - making her 150th WSL appearance - missing a golden chance and Brighton having two penalty appeals waved away in the first half.
Blues keeper Sophie Baggaley, who swapped the south coast for the Midlands in the summer, made eight saves to deny her former team-mates, finally being beaten by Garcia's crisp shot in the 77th minute.
Brighton piled on the pressure but it appeared to be in vain until Seike found an inch of space in the box and crashed into the net to break Birmingham hearts.