Hakim Ziyech lashed Chelsea ahead against the run of play in the 28th minute.
The Blues had struggled to make an impact in the game before Ziyech made space just outside the box to unleash a low, left-footed strike into the bottom-right corner.
Seagulls goalkeeper Robert Sanchez got a hand to the shot and possibly should have kept it out.
Brighton deservedly levelled on the hour courtesy of a thumping header from stand-in captain Adam Webster.
Alexis Mac Allister delivered an inswinging corner from the left and the unmarked Webster powered a header past Chelsea goalkeeper Kepa Arrizabalaga from around eight yards.
Here's who shone and who struggled for Albion against Chelsea.
Rob Sanchez 6: Beaten low at his near post by Hakim Ziyech's long range effort. It was an awkward one as it bounced in front but perhaps could done better. Otherwise sound and a good second half save to deny Lukaku.
Joel Veltman 7: Had his hands full in the first half as Alonso and Mount both looked to attack down his side. Dealt with it well in his usual unfussed manner. Another sound display.
Adam Webster 9: Thumping header for the leveller. Solid defensively and always looking to drive forward and start the Albion attacks. Impressive.
Dan Burn 8: Continued his fine recent form and looks every inch a top level Premier League defender. Enjoyed the physical challenge of Lukaku and formed a good partnership with Webster.
Tariq Lamptey 8: High-octane performance from Lamptey against his former club. Some mesmerising movement and skill and one move where he burst through the entire Chelsea midfield. Eye catching and gave Alonso a tough evening. Subbed on 76 for March.
Pascal Gross 7: Added control and experience to the midfield. Dangerous deliveries from set-pieces and good in possession. Replaced by Maupay on the hour.
Jakub Moder 7: Had an early chance when he shot narrowly wide after linking well with Welbeck. Takes up very good positions in attacking areas.
Steven Alzate 6: Back in the starting line-up and a crucial part of the midfield that was missing Bissouma, Lallana and Mwepu. Solid.
Marc Cucurella 7: Lively presence down the left. Excellent defensively and looked to bomb forward at every opportunity. Another classy display from the Spaniard. What a signing!
Alexis Mac Allister 6: Feisty display from the No 10. Trying to make the most of recent opportunities provided the delivery for Webster's goal.
Danny Welbeck 7: Provided a focal point to Albion's attack. Looked fresh, linked play well and had one shot that flew over after a sharp move cutting in from the left. Went close at the start of the second when he flashed a shot wide. Replaced by Trossard on 62.
Leo Trossard 6: Clever movement and caused Chelsea defenders different problems when he came on.
Neal Maupay 6: Came on with 30 to go but a chance for the winner just did not fall his way.
Solly March 6: Came on for Lamptey and was positive in his play. Took on his defender and always looking to cross.