Brighton came from behind to beat Chelsea and reach the fifth round of the FA Cup.
The Blues took a fortunate lead early on when Cole Palmer’s volleyed cross from the left was fumbled into his own net by Bart Verbruggen.
But Albion came back and Georginio Rutter headed in from Joel Veltman’s cross.
And they took the lead when Rutter picked out Kaoru Mitoma – the subject of a rejected £54m bid from Saudi Arabian side Al-Nassr before the transfer deadline – who dinked the ball over Robert Sanchez.
Chelsea felt the goal should have been disallowed, as the ball struck Tariq Lamptey’s arm in the build-up, though there are no video assistant referees in the FA Cup fourth round.
Those goals came from Albion’s only shots in the first 60 minutes.
Enzo Maresca’s visitors – who fielded a strong side – rarely looked like equalising, with Enzo Fernandez shooting over the bar, and have now gone five away games without victory.
The clubs meet again at Brighton’s Amex Stadium on Friday (20:00 GMT) in the Premier League, where Chelsea are nine points and six places above their cup conquerors.
Brighton bounce back from Forest annihilation
Brighton boss Fabian Hurzeler made only one change from Albion’s last game – the 7-0 thrashing by Nottingham Forest.
His side sit 10th in the league after back-to-back defeats – but they will be delighted to get back to winning ways, and maybe a new focus in the season.
Brighton have never won a major trophy in their history, with the 1983 FA Cup final – which they lost in a replay to Manchester United – as close as they have got.
They were not at their best but they were clinical, scoring with two of their six shots.
Rutter’s equaliser came when he guided a header into the bottom corner moments after former Seagulls keeper Robert Sanchez had unconvincingly dealt with a cross.
Sanchez, Marc Cucurella and Moises Caicedo – especially the former two – were booed on their return to their old home ground.
VAR does not come into the FA Cup until the fifth round, which may be a relief to Brighton.
The ball struck ex-Chelsea defender Lamptey’s arm after his shot was blocked – but there was no denying the quality of Mitoma’s deft touch to knock the ball past Sanchez and ultimately settle the tie.
