OXFORD United put in a magnificent effort as they took West Bromwich Albion all the way to a penalty shoot-out at the Hawthorns.
The Premier League side edged through 7-6 on spot kicks, as skipper Jake Wright saw his effort saved, allowing Jason Davidson to seal the narrowest of victories.
West Brom appeared to be heading for a routine victory as they showed their class early on.
The pressure told when Johnny Mullins scored an own goal on 29 minutes, but United dug in to stay in the tie.
They grew in confidence as the game wore on and levelled four minutes from time when Danny Hylton scored from Will Hoskins's knock-down.
Junior Brown had two good chances to put United in front during extra time, before he was sent off for picking up a second booking.
The visitors held on for penalties, but despite Max Crocombe saving from James Morrison and Brown Ideye, the Baggies came out on top.
United boss Michael Appleton kept faith with the side which started Saturday's 1-0 home defeat to Portsmouth.
His only change was enforced, as Crocombe replaced the ineligible George Long in goal, while new signing Hoskins was named among the substitutes.
The home side made seven changes from their goalless draw at Southampton, but it was far from a weakened side.
Of the XI, eight were senior internationals and another two had caps for England's under 21 side.
They came racing out of the blocks and United needed a vital block from Wright to deny Ideye in the six-yard box after just 15 seconds.
It began a breathless first five minutes, as the visitors struggled to stay on level terms.
Crocombe had to be alert to save Chris Brunt's chested effort from Stephane Sessegnon's cross.
Sessegnon also blasted wide from range with one chance and in the next attack he sliced through to set up Saido Berahino, who was halted by an important challenge from Joe Riley.
It took almost a quarter of an hour for United to launch a raid forward, when a speculative shot from Josh Ruffels was deflected wide.
But midway through the half West Brom went up a gear.
Sessegnon, pulling the strings just behind Ideye, had a sweet shot saved by Crocombe, who a minute later also had to parry from Andre Wisdom.
From the next attack, Wisdom fizzed a low cross into a packed six-yard box, striking the luckless Mullins on the shin and ricocheting past Crocombe into the net.
A lead was justified on the balance of play, but it was a desperately unfortunate way for United to concede.
The visitors, bottom of the Football League, worked hard to limit the chances and managed to reach half-time just one goal adrift.
West Brom looked to kill the tie early in the second half and only a superb tackle from Tom Newey prevented Berahino from a clear run at goal eight minutes after the restart.
But as the game wore on, United began to look a threat and on 66 minutes came a big chance.
Morris collected a long pass and played a sharp one-two with Brown to get in the box, but he dragged the left-footed shot wide.
Match highlights, via Oxford United's Youtube channel
Unbowed, United continued to pass their way back into the game.
Alex Jakubiak replaced Danny Rose in an attacking change and within seconds the substitute had an opening in the box, only to be let down by a poor first touch.
West Brom's growing concern was shown a few minutes later, when Sessegnon came off for the more defensive-minded Youssouf Mulumbu.
Appleton's final roll of the dice was to give Hoskins his debut and within five minutes he made an impact.
Brown got forward and swung the ball to the back post, where Hoskins headed back across goal for Hylton to bundle in from a yard in front of an ecstatic away end.
Berahino had a chance to win it in stoppage time, but Crocombe stood up well to block and send the game into extra time.
When play restarted, Brown had two fantastic chances to put the underdogs in front.
First, Myhill spilled Jakubiak's cross into the winger's path, but he had two shots blocked.
A minute later, Hylton found him in space, but Brown shot straight at Myhill.
The winger was involved again six minutes into the second period, when he collected a second booking for a late tackle on Craig Dawson.
It looked a little harsh on Brown, who appeared to lose his footing and fall into the defender, rather than going in with malice.
United were left to play for penalties and they had a heart-stopping moment a minute from time when Dawson headed in, only for it to be ruled out for a push.
It went to a marathon shoot-out, where Myhill's save from Wright gave Davidson the chance to win it, which the Australia international buried to send the Baggies through.
West Brom (4-2-3-1): Myhill, Wisdom, Dawson, McAuley, Davidson, Yacob, Baird (Gamboa 105), Berahino, Sessegnon (Mulumbu 79), Brunt (Morrison 64), Ideye.
Unused subs: Foster, Olsson, O’Neil, Roofe.
Booked: Oxford Utd (4-2-3-1): Crocombe, Riley, Mullins, Wright, Newey, Collins, Ruffels, Rose, Hylton, Brown, Morris.
Subs used: Hunt (Riley ht), Jakubiak (Rose 70), Hoskins (Morris 81).
Unused subs: Stevens, Meades, Raynes, Potter.
Booked: Brown, Wright, Crocombe.
Sent off: Brown.
Referee: James Adcock (Nottinghamshire).
Attendance: 10,939 (approx 2,000 visitors).