County, while under great pressure at times, had held the lead quite comfortably after Blair Spittal’s first half header before a 61st minute red card for Lewis Spence.
MacIver’s entrance after 74 minutes was followed, just seven minutes later, by a game-changing contribution. After controlling a high ball 25 yards out, he turned with instinctive venom to fire high into the net.
Then, sickeningly for the hosts in the dying seconds of stoppage time, Scotland international Declan Gallagher, pictured, finished the job with a headed winner.
“People get released for all kind of reasons and maybe Ross wasn’t quite good enough at that time,” Motherwell manager Stephen Robinson suggested, fresh from seeing his team’s recovery retain a berth in the third European place.
“Maybe Ross wasn’t quite what Ross County were after. We needed that type of young striker we could develop – and he has.
“He has got the bit between his teeth, tried to pick strikers off and force his way into the team with a great attitude – and he got a lot of rewards today.
“It’s a lesson for all young players that, if you get released, it’s not necessarily the end of the world. Ross has certainly shown a great attitude and appetite.”
The only black spot for Well was the away fans’ behaviour in unsavoury scenes, spilling onto the park after the winner.
Early in the match, they had been in far more friendly and festive mood, roused by Christmas spirits and a strong Motherwell start.
The Fir Park side’s confidence and energy shone with Sherwin Seedorf foraging into spaces on the right and forcing some sharp defending for cross balls, while ex-Caley Thistle midfielder Liam Polworth’s clever passes behind the defence tested County to the max.
James Scott, in particular, looked lively and dangerous, but it was County who went in front after 24 minutes.
After slick County build-up, Richard Foster’s cross from the right was lofted only just too high for the prowling Billy Mckay’s head in front of goal.
But Sean Kelly was eventually able to return the ball from the left and Blair Spittal, making a towering leap eight yards out, bulleted a downward header in off the glove of keeper Mark Gillespie.
It remained lively in the second half, but neither side could gain the upper hand before County’s Lewis Spence blatantly terminated Seedorf’s charge at goal with a trip that earned a straight red card
While the free-kick came to nothing, the one-man disadvantage changed the flow of the game although Motherwell’s assault appeared to be petering out before young MacIver made his entrance.
Taking a high ball at least 25 yards out, the ex-County striker turned and rocketed a shot high beyond the reach of Baxter. Even then, County felt they had a draw within their grasp until the final seconds.
Then came Gallagher’s moment at the death – and County were left flat out on the Boxing Day canvas.