Motherwell's John Sutton netted on either side of half-time to end Celtic's 17-match unbeaten run in Sunday's Scottish Premier League encounter.
The home side were in the lead as early as the second minute when Sutton got on the end of a Charlie Mulgrew mistake to slide home the first.
With the league leaders failing to score it was Motherwell who went in at the break in front and they doubled their lead just four minutes after the restart when Keith Lasley was brought down by Emilio Izaguirre.
Sutton converted the subsequent penalty and that was the way it was to end as Celtic struggled to create any genuine scoring opportunities.
Neil Lennon's side endured the worst possible start when first Chris Humphrey pounced on Mulgrew's attempted clearance before his hesitation allowed Sutton to fire past Fraser Forster in the Celtic goal.
The visitors regrouped quickly and pushed forward but it was Motherwell who had the ball in the back of the net after 18 minutes, only for Sutton's strike to be ruled offside.
Celtic increased the pressure on Motherwell but Anthony Stokes and Scott Brown's efforts were blocked by goalkeeper Darren Randolph.
Motherwell had to wait just four minutes after the restart to double their lead when the referee correctly judged Izaguirre to have fouled Lasley in the box.
Neil Lennon made changes in the hope of getting Celtic back into it, but they made little difference as Motherwell held on to hand the league leaders their first defeat since 10 November.