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.
13. Welbeck 8
What a header. Deserved equaliser and reward for his work to get back to fitness
14. Alzate 6
Late sub and helped Albion to the draw