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.

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Brighton celebrate their leveller at Chelsea

. Sanchez 6
Flapped at a corner on 16 minutes but was saved by the post. Smart save at near post to deny Mount but no chance with Lukaku's header

. Burn 7
At the heart of the defence and stood up well to the Lukau challenge

. Lamptey 6
Lively against his former club in the first half. Played more advanced and always looked to drive forward. Replaced by Mwepu on 65

1. Sanchez 6
Flapped at a corner on 16 minutes but was saved by the post. Smart save at near post to deny Mount but no chance with Lukaku's header

2. Burn 7
At the heart of the defence and stood up well to the Lukau challenge

3. Lamptey 6
Lively against his former club in the first half. Played more advanced and always looked to drive forward. Replaced by Mwepu on 65

4. Veltman 7
On the right of the defence and kept Hudson-Odoi very quiet in the first half. Proved his value to the squad yet again