Motherwell 1-2 Aberdeen
Aberdeen survived a late rally from 10-man Motherwell to move into the Scottish Cup semi-finals thanks to a superb Rory Fallon double.
Fallon headed powerfully home from close range after only five minutes following a hotly disputed corner.
Michael Higdon had a penalty saved by the Dons' Jason Brown before Fallon volleyed home just before the break.
Keith Lasley suffered a 69th-minute red card, but Nick Law's close-range reply ensured an exciting finish.
Lasley, who was being sent off for the third time this season, had returned from suspension to replace Omar Daley in the Motherwell midfield as the home side looked to continue the fine form that has taken them within touching distance of second-top Rangers in the Scottish Premier League.
Aberdeen were denied the services of cup-tied veteran former Scotland international Gavin Rae, whose place was taken in the side by Clark Robertson as they looked to extend their unbeaten run to 13 games.
But, although manager Craig Brown admitted his squad lacked flair, the Dons made a scintilating start to the game and took the lead with a hotly-disputed goal.
Referee Craig Thomson awarded a corner when it looked like the last touch had come from Aberdeen striker Scott Vernon.
When Andrew Considine headed back across the face of goal at the back post, Fallon rose to power the ball past goakeeper Darren Randolph.
Fallon set up another opportunity minutes later, but Vernon headed wide from 12 yards.
Even defender Rory McArdle got in on the act, charging forward before unleashing a powerful drive from 30 yards that was pushed clear by Randolph at full stretch.
Motherwell were more disjointed but gradually forced themselves into the game before winning a penalty when Robertson manhandled Higdon when challenging for a back-post header.
The English striker took the spot-kick himself, but goalkeeper Jason Brown threw himself to his right to parry clear.
Motherwell defender Shaun Hutchinson and Aberdeen utility man Ryan Jack both exited proceedings having failed to recover from an earlier head knock.
Motherwell replacement Jonathan Page did not even expect to be stripped until being called on to the subsitute's bench after Stephen Craigan pulled up in the pre-match warm-up.
The Dons were able to call on Chris Clark and the experienced midfielder soon made his mark.
He sent in a monster of a cross to the back post and Fallon peeled off his marker to fire a beautifully-controlled 16-yard volley flashing past Randolph.
Motherwell manager Stuart McCall, still aggrieved at the opening goal, was sent to the stand after strong words aimed at the referee following the half-time whistle.
Clark and Fallon combined again after the break, when the subsitute's low cross was dummied by the New Zealand international.
It left Mitch Megginson clear in front of goal, but the young forward's drive was blocked instinctively clear by Randolph from point-blank range.
Jamie Murphy, who has been a shadow of the player who was touted for a big-money move last season, fired straight at goalkeeper Brown before being hauled off and replaced with Chris Humphrey.
He was soon followed into the dressing-room by Lasley and Aberdeen's Fraser Fyvie, his team-mate for a high, late challenge that led to the Scotland Under-21 midfielder being stretchered off the field with what looked like a serious leg injury.
The tie appeared to be petering out until Humphrey sped to the bye-line and his low cross slipped under goalkeeper Brown's body and Law was on hand to sidefoot home at the back post.
It was end-to-end stuff in the closing minutes as Motherwell threw caution to the wind.
Kari Arnason cleared a Humphrey drive clear from in front of the visitors' goal before himself stinging Randolph's fingers with a trademark thunderbolt from 30 yards, while Fallon should have done better than chip straight into the goalkeeper's arms.
In a thrilling finish, Law had superb drive pushed away to safety by Brown and, as the goalkeeper's opposite number came up for a last-minute corner, Aberdeen's Peter Pawlett was a foot away from finding the empty net from all of 40 yards.