Millwall were denied victory at the Amex Stadium as Kazenga LuaLua earned the hosts a point with a thunderbolt free-kick two minutes from time.
New signing Andy Keogh's close-range header put the Lions ahead, before the striker dragged a fine chance wide.
Sam Vokes levelled after Alan Navarro's shot was blocked, but goalkeeper Peter Brezovan's error allowed Liam Feeney to recover the Lions' lead.
But LuaLua's set-piece extended his side's unbeaten run to seven matches.
The result could be a valuable one for Gus Poyet's side who are just two points off the play-offs, but it was scant reward for a spirited Millwall display.
The visitors should have been two goals clear after Keogh's opener, but Liam Trotter's 20-yard drive was clawed out by Brezovan before the former Wolves man squandered an excellent close-range chance.
That miss proved costly as Brighton went straight up the other end and Vokes poked home.
Darius Henderson's cross deceived Brezovan as the goalkeeper rushed out and got nothing on the ball to allow Feeney to slot into an empty net for his second goal in three games.
Millwall fell just short of victory though as LuaLua thumped in a searing long-range effort to deny them.
Brighton boss Gus Poyet: "Everything went wrong in this game for us.
"The effort was great but we made so many bad decisions.
"It wasn't a good day, we made too many mistakes. But we threw everything into it towards the end and we came away with a great point. Credit goes to Millwall because I like the way they play."
Millwall boss Kenny Jackett: "I'm sure David is disappointed with the goal.
"I've mixed feelings with the result as we played very well, both defensively and on the ball, and we caused Brighton a lot of problems.
"I'm pleased because we caused Brighton problems and we come away from the game with a lot of positives. I'm frustrated that we didn't get the win having led twice, but the performance in general was an encouraging one."