Marshall had to act on instinct on his introduction to the Premiership and used a considerable array of his tricks as Leeds battled manfully to dig themselves out of the hole they had a large part in creating.
But for Magne, who looked rather bemused at times, it was almost a case of watch and wait for what was to unfold as he attempted to get to grips with the ploys and patterns of his new team-mates, who were putting a fresh game plan into practice.
At least the player who left Clermont Auvergne to see out his career in England had the satisfaction of victory. At the same time, however, he might well have been pondering some confusing facts encountered during his side's four-tries-to-one triumph, most notably that both sides attempted to display their attacking skills and, allowing for a bit of early-season rustiness, played with width and pace.
Contrary to common belief, French club rugby is rarely as adventurous as the stuff Mike Catt and Co employed to see off the Tykes, a factor that another international traveller, the 92-cap Welsh lock Gareth Llewellyn, now of Bristol, has touched upon.
Llewellyn spent last season at Narbonne and left with this thought: "I was surprised at what French club rugby is about; it's different to what you imagine from the French national side. I imagined it would be fast-flowing rugby with width, but in fact it's pretty brutal and direct. In fact, it was just about who had the biggest players to bash open the spaces for the likes of Frédéric Michalak, Yannick Jauzion and Gareth Thomas."
Llewellyn would have enjoyed the sight of Irish's Rodd Penney sprinting 40 metres to score the try that answered Tom Biggs' opening score for Leeds.
But he would not have enjoyed it as much as Magne, who also witnessed Delon Armitage and Justin Bishop crossing the line to put Irish ahead before his back row colleague Kieron Dawson finished off the job in style.
Yet the most entertaining moment belonged to the referee Sean Davey, who added insult to a penalty award by telling a ball-killing Leeds forward: "It's not a beach. Don't lie on it."
Well, he cannot say he was not told.
Leeds: Try Biggs; Penalties Ross 2. London Irish: Tries Penney, Armitage, Bishop, Dawson; Conversions Everitt 2; Penalty Everitt.
Leeds: I Balshaw; A Snyman, C Jones, R De Marigny (T Stimpson, 50), T Biggs; G Ross, J Marshall; J Isaacson (M Cusack, 64), G Bulloch (R Rawlinson, 40), G Kerr, S Hooper (capt; C Murphy, 64), T Palmer, S Morgan, R Parks, J Dunbar.
London Irish: D Armitage; S Staniforth (S Geraghty, 55), R Penney, M Catt (capt), J Bishop, B Everitt, B Willis; N Hatley (M Collins, 40), R Russell (A Flavin, 76), R Hardwick (R Skuse, 40), B Casey, K Roche (R Strudwick, 76), O Magne (Hatley, 62-70), K Dawson, P Murphy (JM Leguizamon, 55).
Referee: S Davey (Sussex).