Ainsworth's strike downs Dons
A goal on the counter-attack from Lionel Ainsworth saw Motherwell leapfrog Aberdeen as they climbed into second spot in the Scottish Premiership with a 1-0 win.
Ainsworth netted early in the second half of a game which the home side just about had the better of but could not make the most of their opportunities.
The Dons had been forced into a change of formation in the absence of a recognised left-back, lining up 3-4-3 with Johnny Hayes coming in on the left of midfield to replace Mark Reynolds, who had started in the full-back position in the 4-3 win at Inverness.
Motherwell continued with on-loan goalkeeper Dan Twardzik in goal, the Dundee man having moved to Fir Park after injuries to regular keepers Gunnar Nielsen and Lee Hollis.
They made two changes from the side that beat St Mirren 3-0. Stephen McManus missed out and was replaced by Fraser Kerr, while Paul Lawson took the place of Iain Vigurs in midfield.
After an even opening period, the Dons could have taken the lead when Niall McGinn popped up on the right to send in a cross for Hayes, who threw himself at the ball but who could only head wide of the target.
John Sutton was forced from the field twice in the opening quarter after a clash of heads with Joe Shaughnessy, the initial treatment the big striker received not quite having stemmed the flow of blood, with stitches eventually required.
That allowed the Dons an advantage, but Stuart McCall's side did a fine job of containing them and forcing them into shots from distance.
Indeed, it was nearly the half-hour mark before Twardzik was forced into serious action, and even then it was a comfortable hold from McGinn's 20-yard effort.
The Steelmen were always a threat, though, and when Michael Hector's burst up the pitch left Aberdeen short at the back, Jamie Langfield did well to hold onto Lawson's long-range effort.
The best chance of the half fell to McGinn in injury time, the striker sent clear by Peter Pawlett and rounding Twardzik, only to see the Czech react well to save his effort.
But just four minutes after the restart, it was the visitors who took the lead following an incisive counter-attack.
Estonian striker Henri Anier broke following a Dons corner, and with the equally pacy Ainsworth providing support, they had the Dons caught two-on-one.
The sole man back, Hayes, did not know whether to stick or twist, eventually moving to block off Anier who calmly squared for Ainsworth to stroke home for the second time in as many games.
Aberdeen responded, and when Pawlett was slipped in by Ryan Jack, the midfielder appeared to be hauled down by Shaun Hutchinson. His furious claims were waved away by the referee, though, and Russell Anderson picked up a booking for dissent in the aftermath.
It also sparked a reaction from the home support who were suddenly loudly behind their team, roaring for every decision and urging their side forward.
And their support was almost rewarded when Shaughnessy popped up on the edge of the area to send a left-foot volley off the outside of the post from 20 yards.
The home side changed formation, but were almost caught by another counter, Twardzik's clearance finding Anier who was denied only by a desperate block from Shaughnessy.
That would be the striker's last involvement, as he was replaced in attack by Craig Moore.
Trading changes, the Dons brought on Josh Magennis for Shaughnessy, before Motherwell's Zaine Fracis-Angol took the place of Ainsworth.
Aberdeen's last throw of the dice saw them replace Scott Vernon and the injured Barry Robson with Craig Murray and Calvin Zola after 84 minutes.
The visitors battled for every scrap, but they had a scare deep into injury time when the crowd thought McGinn had levelled matters with a free-kick which had in fact only hit the side-netting.