A first-half header from Nigerian centre-back Danny Shittu gave Millwall a 1-0 win at Blackburn Rovers that set up an FA Cup semi-final at Wembley against Wigan Athletic.
Shittu, the Millwall captain, struck shortly before half-time to settle the quarter-final tie, three days on from the hard-fought 0-0 draw between the Championship rivals at the Den on Sunday.
"Words can't really describe it," Shittu said.
"We just wanted to come here today and win. To have got the goal, it means so much. I'm just happy for the lads and for the gaffer."
Millwall are the last non-Premier League side in the competition and hope to emulate their run to the final in 2004, when they lost 3-0 to Manchester United. United will face Chelsea in the second quarter-final replay on April 1, and the winners will meet Manchester City.
A disappointing crowd of under 9,000 witnessed the home side procure the first sight of goal at Ewood Park, but Leon Best's low shot was comfortably saved by David Forde.
The recalled David Dunn, making his first start since October, then swept a shot wide from a corner, but as the half progressed, Millwall began to assert themselves.
Chris Taylor lashed a shot narrowly off-target from 20 yards midway through the first half, before the breakthrough arrived three minutes from half-time.
Millwall had just seen a penalty appeal for handball against Jason Lowe dismissed when Taylor swung a corner into the box from the left that the strapping Shittu converted with a powerful downward header.
It was the first time that Blackburn, owned by Indian poultry firm Venky's, had conceded a goal in this season's competition.
Rovers coach Michael Appleton introduced Portuguese veteran striker Nuno Gomes at half-time, but the hosts had to wait almost 20 minutes to fashion a chance.
When it came, Millwall were indebted to a superb goal-line clearance from Shane Lowry to deny Best, who had eluded a couple of challenges before dispatching a low drive that beat Forde.
Taylor could have sealed victory when he hoisted a shot over the bar from 12 yards in injury time, but the hosts came no closer to forcing extra time and left the pitch to a volley of boos.
"We huffed, and we puffed, but it just didn't drop for us on the evening," said Appleton.