From the Amex Stadium - Brighton effectively extinguished Chelsea's slim title hopes on Tuesday night by holding the Blues to a second 1-1 draw in a matter of weeks at the Amex Stadium.
Despite an incredibly disjointed first half where they were second best throughout, Chelsea found themselves ahead at the break.
Brighton started the game on the front foot and almost had the lead inside three minutes, but Jakub Moder's low shot slid just wide of Kepa Arrizabalaga's far post.
Penned back by their energetic hosts, Chelsea couldn't muster a shot in anger until a quarter of an hour had passed. The Blues broke, and Romelu Lukaku's lay-off was fired towards the top corner by Cesar Azpilicueta, but his international teammate Robert Sanchez was able to get a firm palm to the ball.
However, the keeper's wrists suffered some ill-timed floppiness shortly before the half-hour mark. Hakim Ziyech's crisp drive beat him at his near post as Chelsea took the lead against the run of play.
The visitors just about found their feet thereafter and should have doubled their lead on the stroke of half-time, but Callum Hudson-Odoi lacked composure after being played in by Lukaku and blazed his shot over.
Brighton were deservedly level on the hour mark. Alexis Mac Allister's deflected shot was brilliantly clawed away by Kepa, but Adam Webster met the resulting corner unmarked and sent a bullet header into the back of the net.
Marcos Alonso blasted a long-range strike narrowly over the bar as Chelsea sought to restore their advantage immediately, but Brighton remained in the ascendancy. Substitute Neal Maupay spurned a trio of decent half-chances for the winner, including misjudging Tariq Lamptey's pull-back and letting a through-ball hit his heels as he was slipped in on goal.
Both sides huffed and puffed as the game became stretched late on, but neither could find a winner.
The result leaves Chelsea two points behind Liverpool in second in the Premier League having played two games more and 12 behind leaders Man City, who have a game in hand too. Brighton stay ninth.
Brighton player ratings
1. Goalkeeper & defenders
Robert Sanchez (GK) - 5/10 - Caught cold by Ziyech's low blast - should probably have done better.
Joel Veltman (CB) - 6/10 - Solid enough in an unfamiliar centre-back role.
Adam Webster (CB) - 9/10 - His ball-carrying and passing ability out from the back kept his side on the front foot. Brilliant bullet header to level, although he was afforded acres of space. Wonderful tackling too. Top, top notch.
Dan Burn (CB) - 7/10 - Barely gave Lukaku an inch whenever he attempted to spin in behind - exemplified by an excellent crashing challenge after the break.
2. Wing-backs & midfielders
Tariq Lamptey (RWB) - 7/10 - A real menace down Brighton's right as he looked to show his former club what they're missing. Electrifying before being subbed.
Pascal Gross (CM) - 5/10 - Quiet in the middle of the park but got through plenty of running.
Steven Alzate (CM) - 6/10 - Charged with hassling Jorginho and did very a good job for the most part. Tired late on.
Marc Cucurella (LWB) - 7/10 - Really industrious up and down the left, causing Chelsea problems throughout as he supported the attack.
Jakub Moder (RF) - 6/10 - Sent an early effort just wide of Kepa's post. Industrious but quiet.
Danny Welbeck (ST) - 6/10 - A willing runner but couldn't take advantage of his one half-opening. Subbed.
Alexis Mac Allister (LF) - 7/10 - Saw his deflected shot clawed away by Kepa seconds before the equaliser, which came from his corner.
Neal Maupay (ST) - 5/10 - Missed three half-decent opportunities to give the Seagulls the lead after his introduction.
Leandro Trossard (LF) - 6/10 - Showed some smart footwork.
Solly March (RWB) - N/A
Chelsea player ratings
5. Goalkeeper & defenders
Kepa Arrizabalaga (GK) - 6/10 - Made a ridiculous save at 1-0, only to be beaten from the resulting corner. Let down by the marking.
Cesar Azpilicueta (CB) - 5/10 - Struggled with the threat of Marc Cucurella and was unable to do his usual overlapping.
Thiago Silva (CB) - 6/10 - Very solid and typically stout until he was one of many Chelsea defenders to lose Webster at a corner.
Antonio Rudiger (CB) - 5/10 - Not at his best as Lamptey had some joy down his flank. His forward runs were lacking.
6. Wing-backs & midfielders
Callum Hudson-Odoi (RWB) - 4/10 - Spurned an excellent chance to double the lead in a poor first period.
N'Golo Kante (CM) - 6/10 - Infinitely energetic and influential as per usual, carrying Chelsea's midfield in the first half. Rewarded with a simple assist for Ziyech.
Jorginho (CM) - 4/10 - Uncharacteristically loose in possession as the hosts harried him in the first half.
Marcos Alonso (LWB) - 5/10 - Struggled against Lamptey's pace and was booked for a clumsy challenge on him.
Mason Mount (RF) - 4/10 - Looked out of sorts in a slightly chaotic display. Barely got into the game. One of three players who didn't mark anyone for the equaliser.
Romelu Lukaku (CF) - 5/10 - Ran hard and saw one shot saved but nothing came off for him.
Hakim Ziyech (LF) - 6/10 - Pretty poor before an unerring low thump beat Sanchez to open the scoring. That gave him confidence, as he showed some nice touches and sprayed the ball about.
Mateo Kovacic (CM) - N/A
Kai Havertz (ST) - N/A
Timo Werner (LF) - 5/10 - Looks like he's lost a few yards of pace.