Lukaku headed Chelsea into a 1-0 lead on 27 minutes, turning in a corner in style.
The Belgium hitman shrugged off Neal Maupay’s measly challenge, with the Brighton’s striker’s protests dismissed without issue by the officials.
Chelsea’s lead eased their latest injury frustration, with Reece James hobbling off with a suspected knee problem.
Albion had decent spells as Adam Lallana and Alexis Mac Allister both forced Mendy into action while Tariq Lamptey was a lively presence on the right.
Danny Welbeck headed Brighton level at 1-1 in added time. The former Arsenal striker nodded home to sting Chelsea, with the angry home fans throwing a blue smoke bomb onto the pitch.
Here's how the Albion players rated.
5. Cucurella 7
Alert defending early on and even outjumped Lukaku on one occasion to clear with a header. Never stops working and adapted well to different defensive role on left side of the three
6. Bissouma 8
Brighton's best player. Great display. Broke up numerous Chelsea attacks and always looking to intercept deliveries into Lukaku and drove forward well.
7. Lallana 6
Lively in midfield and one stinging left footed effort well saved by Mendy. Fired a great chance over the bar in the second half
8. March 6
Played left wing back but struggled to get into the game in first half but looked lively in the second. Steady supply of crosses