While Lee Dixon, sat beside him, was calmly objective about the referee's incoherent decision, former legend Keane stuck the knife into the club that feted him and Nani when he could have been more diplomatic.
Said Keane of Nani's controversial red card:
I think the referee has actually made the right call. Everyone's upset about it and it's slightly unlucky, but it's dangerous play. Whether he meant it or not is irrelevant. It's dangerous play—it's a red card.
...Nani's a quick boy to go down anyway. He's not the bravest player on the planet.
Of course ITV want good television, but the referee and the two teams had already achieved that. It seemed that both presenter Adrian Chiles and pundit Gareth Southgate were somewhat "gobsmacked" as Keane committed a foul much worse than any he dished out on a football pitch.
And why did he have to do it?
Gary Neville has won massive respect for the objective way he reviews and comments on former opponents.
In complete contrast, Keane is, of course, opinionated, which is what the broadcasters want, but he left viewers in no doubt last night that he is "bitter and twisted" about his departure from United, despite his denials.
Indeed his comments ranked not far behind the incident that had provoked them in the first place.
In other circumstances you could understand a pundit bending over backwards to try and seem fair. Keane could have said something like:
"Its an unfortunate decision and Nani might reflect on the wisdom of carrying through his attempt to win the ball, but his eyes are only on the ball and the referee didn't need to give a red card..."
Instead Keane not only became the only person in the media to declare his unequivocal support for the decision, but went further in dishing Nani and United's performance overall.
Hero to zero
It was OK while Roy was giving his all for United and leaving every last ounce of blood, sweat and tears on the pitch. And maybe Sir Alex Ferguson was one of the few managers who could save him from himself, otherwise he might have turned out like Joey Barton.
But when you look into the cold hard facts and set aside any loyalty to a former United player, there is more than enough evidence that Roy Keane was an accident waiting to happen.
Even without mentioning his deliberate attempt to hurt Alf-Inge Haaland (how out of control do you have to be to wait so long to deliberately hurt a fellow professional?), there have been warning signs in the past.
Keane not only fell out with Ireland manager Mick McCarthy, but publicly criticised his country's footballing arrangements.
Now in different circumstances the Haaland affair might have horrified and shamed United fans and the club, but unfortunately for the player who played only 48 minutes more before being forced to retire, he was on the books of Manchester City.
Re-reading all of the events and the chronicle leaves me feeling ashamed to have lauded Keane in the past.
It seems he showed his true colours last night. Where he could have been diplomatic without actually supporting United, just like the referee he made a cold, hard decision to punish them.
Cause and effect
It would be all too easy to explain away Keane's resentment based on his perception of his departure from Old Trafford.
At the time, it was stage-managed by all parties concerned, but the perception was that Keane's outburst against his own teammates on MUTV was the final straw in an already foundering relationship with Sir Alex.
Since his departure as a player, Keane has done little to seek to repair any burned bridges. Indeed he seems bent on the exact opposite, as his renewed attack in May 2012 suggests.
Sadly these are far from being the only public outbursts of this sad man, most of which have been against the club that paid his wages.
So we may safely assume that he is "persona non grata" at Old Trafford, despite his opposite view.
The greatest disappointment about his graceless utterances last night is that Roy Keane has been most famously lauded at Old Trafford for his Champions League exploits.
Most notably, the Juventus return tie in 1999 where he selflessly drove United to an unlikely win and a triumphant final that he knew he would miss.
So how could he sit so charmlessly and cold-bloodedly in judgement of the team, the players and the fans that gave him his livelihood and his adulation?
On Tuesday night he chewed up and spat out that loyalty in a mindless rant that will never be forgotten or forgiven.
After that final and damning act of disloyalty, don't be surprised if United fans not only disown Roy Keane but even have a bad-mouth chant against him as early as Sunday.
The greatest sadness last night was the complete contrast between Keane's behaviour and the gracious and humble return of Cristiano Ronaldo.
While the latter may well be welcomed back with open arms and even thumped his chest in loyalty to his former supporters, Keane would do well to steer clear of M16 for the foreseeable future.