It had been two years to the day since Motherwell last beat them and how the locals revelled in the hard-fought victory their side carved out at Fir Park. So what that 19 points separate the teams? The hosts imposed themselves on Celtic and proved a point to themselves after poor recent form and a horrendous going-over by Ross County at the weekend. A handful of teams are jockeying for second place in the Clydesdale Bank Premier League but Motherwell are perched there now.
Eight consecutive defeats to Celtic amounted to a prolonged spell of pain but they capitalised on poor defending to score through Chris Humphrey and Michael Higdon, the latter claiming his 19th of the season after Georgios Samaras had equalised. Most impressive of all was their hungry, driving midfielder Nicky Law, whose performance eclipsed that of everyone else on the field.
No lasting damage was done to Celtic but after a spell of solid form this was their fifth league defeat of the season, and a mediocre, deeply unimpressive performance from start to finish.
This was Motherwell's night. James McFadden was in their team from the start having appeared as a second-half substitute in their two previous games. He took up his familiar berth on the left of the midfield, operating in a pocket of space between James Forrest, Biram Kayal and Adam Matthews.
It will be a wee while yet before McFadden has shaken off the cobwebs to the extent he can illuminate the play but this brisk, open match did him no harm. There was a wee ripple around the stands whenever he had the ball at his feet. After 71 quietly encouraging minutes he came off to warm applause from the home fans among the 8641 crowd. Law stole his thunder, though. He burst forward down the left and twisted Victor Wanyama before flashing the ball across goal to the foot of the far post where it was rammed into the net by Humphrey.
Celtic had been ordinary in the first half of their weekend defeat of Dundee and then improved. Not this time. Too often their attacks broke down and passes were intercepted. Players did not read each other's movement. Samaras was back in the team after injury kept him out for a month and he was predictably short of sharpness, but that was nothing compared to Anthony Stokes' contribution. One of his efforts zipped off his standing leg and flew out back towards his own half rather than to Darren Randolph's goal. A later effort was barely any better.
Celtic played 4-2-3-1 in the first half and then pushed Samaras from midfield to join Stokes in the front line. Kris Commons bent a decent chance into Randolph's arms and when Stokes finally came good and clipped a ball across for Commons he was shepherded wide and away from danger by Randolph. Tom Rogic brings a certain poise to the Celtic midfield but this match passed him by and Joe Ledley replaced him early in the second half.
Kayal had been far more involved, scrapping away tenaciously, but after a first-half booking Lennon withdrew him after an hour to avoid a potential red card.
There was little change to the scrappy, untidy pattern of the overall play but pressure was building from Celtic and their equaliser was predictable. Forrest dug out a fine cross from the right and the delivery was expertly met and headed in by Samaras.
Still, Law was full of energy and dynamism, eager not only to get the ball but do something with it. Having created the first goal he repeated the feat to put Motherwell ahead again, turning Efe Ambrose inside out before placing a cross over Emilio Izaguirre to the boot of Higdon at the back post. The big fella rammed a finish high into the net.
Celtic were without Scott Brown, Kelvin Wilson, Mikael Lustig and Charlie Mulgrew while Ledley, Ambrose and Gary Hooper helped comprise a heavyweight substitutes' bench before all three were used. Hooper's low ball to Ledley would have brought an equaliser had Randolph not smothered his shot.
It will be horses for courses in the remaining fixtures of the season and most of the available thoroughbreds inevitably will be deployed from the start in the next two fixtures, against St Mirren in the Scottish Cup quarter-final this weekend and Juventus in the Champions League in Turin on Wednesday. Europe is a lost cause but the Scottish Cup tie will help shape the remainder of Celtic's season. Having gone out of one cup to St Mirren already, to go out of a second would seem unpardonable.