Occupying the hot seat at such short notice is a tough challenge for any broadcaster, and especially one who has had to weather more than his own share of brickbats for his sometimes misfiring forays into TV.
Bunny Carr never had to endure such heavy scrutiny from the media and the public when he occasionally stood in for Gay Byrne in the old days. But an opportunity is an opportunity and Ryan rose to the challenge admirably.
To use an expression one feels more comfortable using in relation to Ryan than to Kenny, Gerry grabbed the show by the balls and gave it a good shake.
For the viewer, it was initially a strange spectacle. Once the familiar theme music and the familiar title sequence ended, we knew who would be walking on to that familiar set. Yet somehow it still seemed ever so slightly surreal.
Gerry himself acknowledged how strange it all felt, and from the outset the tone of the show was different.
The audience, as revved up with curiosity and anticipation as the rest of us, gave Gerry a rapturous reception that somehow seemed more spontaneous, more genuine, than the usual stage-managed applause studio floor managers whip up at the beginning of a show. There was a touch of the party atmosphere about the whole thing.
Gerry landed on his feet with his first guest, Tony Curtis, one of the last surviving members of old Hollywood movie-star royalty and, as guests go, right up Gerry's alley.
Curtis, who has just published his autobiography, looked frail -- worse, even, than when he appeared on Graham Norton's BBC show a few months ago -- and had to be helped to his seat by his wife of 15 years.
But his head, concealed beneath a huge Stetson hat, is still in perfect working order and he has a fund of salty stories to tell -- about working with Marilyn Monroe on Some Like It Hot and about his own devastating cocaine problems. Gerry, whose style is looser, more raucous and more blokey than Pat Kenny's, revelled in the tales.
He looked relaxed and at home, even if it was someone else's home he was relaxing in. Curtis, too, seemed to be enjoying himself and, as he's been known to do on many a chatshow appearance, playfully upended the interview.
"Tell me a little about yourself," he asked Gerry. "What were you like when you were 17?" "I had long hair and I was an idiot," said Gerry.
"You're a good guy," said Curtis. "And you're a GREAT guy! Are you impressed?" said Gerry, turning to the audience. He meant with Tony Curtis, of course, but he was doing a pretty impressive job himself.
There was a suspicion that the line-up of guests had been slanted towards the lighter end of things, to fit Gerry's particular talents.
But there's nothing wrong with this. Friday nights were built for light entertainment and if anything, that's something the current season of the Late Late has been lacking.
Overall, there was a strong line-up of guests. Richard Madeley, who came across as a more ruminative man than he appears on the easy-going teatime shows he co-hosts with his wife Judy Finnigan, spoke movingly about his otherwise loving father subjecting him to physical abuse.
Gerry, who is particularly good on his radio show with sensitive topics, handled this particularly well, letting Madeley do the most of the talking.
His interview with his final guest, comedian Roseanne Barr, wasn't as sparky as it could have been. This, though, had less to do with Gerry than with surprisingly dreary Roseanne.
The one part where Gerry lost his grip somewhat was when Tommy Tiernan came on -- and who wouldn't? Tiernan is a chaotic force of nature at the best of times, but here he was in flat-out mischief mode.
Tiernan embarked on a string of outrageous gags about Travellers, and there's little any host could do in that situation except sit back and wait for the Tiernan hurricane to pass. And that's what Gerry Ryan did.
The question everyone wants answered is: Was Ryan a credible host? Yes, he was.
He did an extremely good job in a tricky situation. We might just have had a small glimpse of Mr Ryan's future direction, if he's up for it.