Tom Hateley headed home Jamie Murphy's cross after 10 minutes to give Stuart McCall's side the lead against the run of play.
The hosts again punished Aberdeen's failure to take their chances as Murphy doubled their advantage on the half-hour mark, however Jonny Hayes powered through the midfield before powering an effort past Darren Randolph to reduce the deficit just minutes later.
Murphy notched his 10th goal of the season on the stroke of half-time to provide a timely boost for Well and Michael Higdon added a fourth 10 minutes into the second half.
Former Scotland Under-21 international Murphy was handed a chance to complete his hat-trick when Motherwell were awarded a penalty with 25 minutes remaining, but his weak effort was saved by Jamie Langfield.
The visitors passed up a glorious opportunity to open the scoring after three minutes when Niall McGinn drilled wide after Randolph had blocked from Joe Shaughnessy.
Motherwell burst into life after six minutes when Nicky Law rattled Langfield's bar with a fizzing effort from the edge of the area, and the opening goal arrived three minutes later when Murphy's precise delivery was headed beyond Langfield by Hateley.
Despite enjoying the better of the possession and chances Aberdeen were again punished for their lack of cutting edge on the half-hour mark as Murphy drove into the box before angling a low shot past the despairing Langfield.
Motherwell were not to enjoy their two-goal advantage for long as Hayes burst through the midfield before powering a shot low into the bottom left-hand corner.
The home side got the perfect lift on the stroke of half-time as Murphy slotted home his second of the afternoon.
Higdon was the first player to receive a yellow card for a careless lunge on Mark Reynolds. The former St Mirren striker was celebrating shortly afterwards however - as he slid the ball home after some fantastic build-up play from Ojamaa.
It was Motherwell who looked the more likely to add to their tally though and they were awarded a penalty when Ojamaa was tripped inside the area by Clark Robertson, Murphy stepped up hoping to seal his hat-trick, but was denied by Langfield.
The closing minutes brought little in the way of goalmouth action and Motherwell held on for a victory that moves them level on points with Inverness in second place in the league table.