Brighton required extra time to seal their spot in the fourth round of the FA Cup as Neal Maupay's 97th minute strike completed a 2-1 comeback victory against West Brom.
The Seagulls ought to have taken the lead on 18 minutes when Danny Welbeck was sent through by Solly March, but the former Arsenal man couldn't find his balance and stabbed his effort straight at West Brom goalkeeper David Button.
The home side briefly threatened the Brighton goal shortly after. Matt Phillips did well on the edge of the area before playing in an onrushing Jake Livermore, but the midfielder's effort was blocked out for a corner.
The half ended with a late flurry from Brighton, which should have seen Graham Potter's side rewarded. Maupay went close with a looping header when Odel Offiah returned the ball back into the area from a corner.
The Frenchman then went even closer when a mix-up in the Baggies defence allowed Welbeck to free his strike partner but, with just Button to beat, the forward could not break the deadlock.
The Seagulls were made to pay just 90 seconds into the second period when West Brom put themselves ahead.
Phillips was quicker to the loose ball than Shane Duffy and his headed flick sent Karlan Grant through on goal. The 24-year-old, haring towards goal, lifted his head and rolled the ball across to Callum Robinson at the far post who prodded into the back of the net.
Brighton were handed a lifeline with just over 20 minutes to play when West Brom defender Cedric Kipre was given his marching orders. Just seconds after he was booked for a foul on Maupay, the 25-year-old could have no complaints when he hauled down Leandro Trossard in a promising position for his second yellow card.
From the resulting free-kick, Duffy volleyed over from point-blank range to increase the frustrations among the travelling Seagulls faithful.
However, Brighton's patience was rewarded with ten minutes remaining when two of Potter's substitutes combined. The Seagulls linked neatly from a Marc Cucurella infield pass and when Jakub Moder latched onto Evan Ferguson's pass, the Poland international smashed his effort beyond Button at his near post to send the contest into extra time.
West Brom were visibly flagging as they wrestled with their man disadvantage, and Brighton ruefully punished them just seven minutes into extra time.
Moder - whose introduction swung the game in Brighton's favour - passed across goal and Maupay swept the ball into the bottom corner after a clever dummy from Trossard to fool the Baggies defence.
Ferguson thought he had added a third for Brighton just minutes later when he bundled the ball over the line from a Moder strike across goal, but the linesman was quick to raise his flag for offside as the Seagulls saw the rest of the game out.
Here's how Potter's men rated.
Brighton player ratings
1. Goalkeeper & defenders
Kjell Scherpen (GK) - 5/10 - Could do little to prevent West Brom's opener.
Joel Veltman (CB) - 7/10 - Brighton were strong down their right hand side thanks to the Dutchman's defensive assurance.
Shane Duffy (CB) - 3/10 - His lack of mobility was exposed for West Brom's opening goal.
Dan Burn (CB) - 4/10 - A galloping presence down the left hand side, but he was slow to react in the lead up to West Brom's goal.
2. Wing backs & midfielders
Odel Offiah (RWB) - 4/10 - Deployed in an unfamiliar wing-back role, showing some bright flashes.
Enock Mwepu (CM) - N/A - Forced off after 25 minutes holding his hamstring.
Pascal Gross (CM) - 6/10 - Kept Brighton ticking in midfield, but he was easily contained by West Brom.
Steven Alzate (CM) - 7/10 - A dynamic presence in midfield, always looking to run beyond the West Brom backline.
Solly March (LWB) - 7/10 - Accomplished performance, taking the care of the ball in tight areas to allow Brighton to break through West Brom's pressure.
Danny Welbeck (ST) - 4/10 - His energy in the forward line was useful, but he lacked sharpness in front of goal.
Neal Maupay (ST) - 6/10 - Spurned a promising one-on-one opportunity in the first half, but he made amends in extra time.
Alexis Mac Allister (CM) - 6/10 - A lively presence, but his decision making in the final third was absent.
Marc Cucurella (LWB) - 6/10 - Made an instant impact, driving to the byline to create a good opening for the Seagulls.
Leandro Trossard (ST) - 7/10 - His pace prompted Kipre's red card in the second half and his lovely dummied assisted Maupay's extra time strike.
Evan Ferguson (CM) - 7/10 - The Seagulls faithful were chanting his name after a superb cameo.
Jakub Moder (ST) - 9/10 - His introduction spared Brighton's blushes, scoring and assisting either side of the full time whistle.