Shifted to centre from full-back, the versatile ace kicked all 21 of the reigning GUINNESS PRO12 champions points against Castres Olympique.
And while the French hosts scored the game's only try, Madigan's right boot was enough for O'Connor's troops to seal the win.
"We came with a definite plan to play for field position and take our points when they were on offer," O'Connor said. "Ian was outstanding, he took his goals brilliantly.
"He's a quality goal-kicker and he's playing very, very good footie for us in that No 12 shirt. He looks very comfortable in it.
"There was a little bit of a lack of shape, but it takes its toll when you're playing against humans that big.
"The win was the important thing. We probably didn't get enough dominance at set-piece, we didn't get the ball on our terms and from that end we were chasing the game. We probably didn't have enough momentum to construct anything."
Elsewhere for GUINNESS PRO12 sides in the Champions Cup there were victories for Munster, Glasgow Warriors and Scarlets.
Munster had replacement prop Dave Kilcoyne to thank after he climbed off the bench to barge his way over at the back of a driving maul to score the game's only try in a 14-3 win over Saracens.
Ian Keatley's radar from the kicking tee was slightly off, the fly-half only making two of six attempts at goal, but head coach Anthony Foley was full of praise for his No.10's showing.
"I thought he controlled the game very well. He managed territory and he managed to keep composed and keep the pressure on them. Look he missed a few shots at goal. He will be more disappointed in that than I will be, and I'll try to make sure he understands that's not the end of the world.
"I played with a number of outhalves who missed kicks. Ronan O'Gara and David Humphreys missed kicks at goal, Jonathan Sexton missed kicks at goal. It's part and parcel of having the responsibility of having the shots at goal. Some weeks they go for you. He'll go away and work harder and he'll come back and he'll learn from it."
Gregor Townsend's Glasgow are also sitting pretty with two wins from two, following their destruction of Bath last weekend with an impressive 15-12 win in Montpellier, all the points coming from the boot off Finn Russell.
Scarlets were very clinical in their victory over Leicester, the Welsh region making the most of some poor Tigers mistakes to run in two tries through Aled Davies and Harry Robinson to secure a 15-3 win.
It was less good news for Ulster who found defending two-time champions Toulon too hot to handle in slipping to a 23-13 defeat, Craig Gilroy claiming a late consolation score at the Kingspan Stadium.
Ospreys' unbeaten start in the GUINNESS PRO12 was made to count for little against Northampton, George North running in four tries as the Saints wrapped up a comfortable 34-6 win.
And Benetton Treviso fought hard in their clash with Racing Metro but despite a score from Ludovico Nitoglia they were eventually beaten 26-10 by their French opponents.
In the European Challenge Cup Cardiff Blues continued their winning start with a 33-18 victory against Rovigo.
Newport Gwent Dragons let a half-time lead slip to fall to a 26-20 defeat against Newcastle Falcons and Connacht slipped to a 33-13 loss against Exeter Chiefs.
And finally Edinburgh beat Lyon 25-17, Jack Cuthbert scoring his side's only try to go with 20 points from the boot of Tom Heathcote and Zebre claimed the first European win in their campaign with a 26-21 victory at Brive.
Kelly Haimona and Valerio Bernabo scored tries for the visitors, while fly-half Edoardo Padovani converted both tries and added four penalties.
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