The on-loan Blackburn striker, making his first start for the Fir Park club, turned home a Chris Humphrey cross from close range nine minutes before the interval.
It proved sufficient to settle a game largely lacking in real goalmouth action.
Manuel Pascali was denied a last-minute equaliser by an excellent Darren Randolph save, leaving Kilmarnock still searching for their first points of the campaign.
Craig Brown had one eye on Europe as he made four changes to his Motherwell side. Captain Stephen Craigan dropped to the bench along with Keith Lasley and Jamie Murphy, while striker John Sutton was left out of the squad altogether ahead of Thursday's delicately-poised Europa League playoff second leg against Odense.
The quartet were replaced in the starting line-up by Blackman, Esteban Casagolda, Marc Fitzpatrick and Jonathan Page.
New Kilmarnock defender Mohamadou Sissoko was handed a debut, replacing the benched Liam Kelly as the only adjustment to the Rugby Park side for Mixu Paatelainen's first home game.
Chances were at something of a premium in the opening stages, but the hosts carved the first of the game on nine minutes when James Dayton took possession on the right and made a good run to the byline, crossing for David Silva, only to see him head over the bar.
Danny Invincibile then did well to keep control and possession of the ball at the left corner, and Silva weaved inside to try a drive which ended up well off target.
Motherwell had their first shot shortly afterwards through Blackman, who fired narrowly over Cameron Bell's crossbar.
While the opening quarter was lively and featured some useful wing play from Dayton and Chris Humphrey, it lacked any dangerous penalty-box incursions from either side.
On the half-hour, Jamie Hamill fired in a cross from the right and Silva rose for a header which again finished off target.
The Portuguese player weaved inside once again moments later but his shot was put out for a corner after being cleared by an impressive diving header from Steven Saunders.
It was Motherwell who finally gave the game a much-needed goal nine minutes from the interval, Blackman breaking the deadlock by turning in a far-post cross from Humphrey which had been helped along the face of goal by strike partner Casagolda.
Craig Bryson immediately came close at the other end when he met a cross, only for Mark Reynolds to clear close to the line.
Randolph and James Fowler were both booked for a fracas as the players headed down the tunnel at the interval after tempers had frayed towards the end of the first half.
Kilmarnock attempted to find a route to goal to equalise after the break, but were frustrated first when Silva was flagged offside after being picked out by Fowler, and then when Invincibile tumbled under the challenge of Reynolds in the box.
Blackman carved a chance for himself when he kept possession and squeezed past Frazer Wright on the right touchline and bore down on goal, but his effort failed to trouble Bell in the home goal.
Motherwell then saw Humphrey send in another cross on the hour which Fitzpatrick swept goalwards, but Bell comfortably gathered.
Kilmarnock replaced Fowler with forward Conor Sammon just after the hour in pursuit of an equaliser, and it coincided with their best spell of pressure, including Dayton worrying the visiting defence with a swinging effort at the right-hand post in a busy box.
The hosts again came close when Hamill dispossessed Saunders and crossed from the left for Sammon, but Randolph smothered the ball before Invincibile could race in to bundle home.
Neither side looked likely to score again until a late flurry from both sides in the closing minutes.
The hosts had two corners five minutes from time, but the second saw substitute Liam Kelly head wide from Dayton's delivery from the right, while Tom Hateley tried a late curling strike for Motherwell but saw it beaten to safety by the home goalkeeper.
Manuel Pascali almost rescued a point for Kilmarnock with a tremendous effort following a short corner routine in the 90th minute, but Randolph produced a superb reflex block to seal his side's win.