Not bad for a "tiring" side, as England's Eddie Jones called them. Instead, Wales were composed and concise, imperious and implacable. Ireland looked so unhappy you wondered whether they spent the whole week at the Cheltenham Festival, and backed a loser in every race. At least part of the reason for Ireland's hopelessness was Wales' ruthless intent from the start. No team can achieve such wins - no side can win a Grand Slam - without brilliant guidance from the helm.
In a country of myths and legends, of folk hero fly-halves and daring wingers, Gatland has attained immortality by harnessing the latent emotional force of Welsh rugby and adding tactical shrewdness and hard-headedness. "I've got to have that belief and self-confidence in ourselves, and if I can project that onto the players in some way then hopefully they can believe it as well," he said.
The tight game we all expected went out of the window in the second minute when Gareth Anscombe chipped ahead for Hadleigh Parkes to touch down. Only in the dying seconds did Ireland put points on the board and spoil the perfect numbers of Gatland's last Six Nations outing with Wales.
After the comeback win in Paris, he said: "We've become a side that's probably forgotten how to lose." Fightbacks against France should carry an asterisk to account for French flakiness, but Wales' told a story about them, and Gatland, as well as the eccentricity of the hosts. Gatland sent them out in the Cardiff rain without any sign that they had even considered the possibility the Grand Slam might be in jeopardy.
"To be 12 years as an international coach - I've done six and it's nearly killed me, so I don't know how Gats has done 12," said Joe Schmit, Ireland's beaten coach. Nobody knows where Gatland will turn up next but the end of the road with Wales is still a long way off. A colossal challenge looms. Wales, remember, have never reached a World Cup final, though they came close eight years ago, losing a semi-final 9-8 to France. A third-place finish in the inaugural tournament, in 1987, remains the high water mark for a nation now ranked No 2 in the world for the first time in their history.
Alun Wyn Jones, whose leg was twisted into a position a contortionist would have envied - but somehow shook off the resulting injury - was the first to acknowledge that Wales can no longer slip into Japan this autumn as dark horses. "We've got to be aware that we've put a target on our backs," said Jones, whose physical contribution in this game alone justified Jonathan Davies' description of him as one of the all-time great Welshmen.
In a perfect world for Wales, the final stop on the Warren Gatland farewell tour would be Yokohama, Japan, on November 2, in the 2019 World Cup final.
Gatland's work with Wales and the British and Irish Lions already entitles him to place in the coaching pantheon. But there is another level up from this, remarkably. Another grade higher than Grand Slams. And in this Welsh performance you saw the improved "game management" Alun Wyn Jones talked about as a vital pre-requisite for success. You saw hope for Japan.
At the end Gatland wiped away a tear. Either that, or rain in his eyes. On the press conference platform, Alun Wyn Jones told us: "I don't want to be too romantic with him sitting here, but he alluded to the fact that when you've got someone so confident sitting at the top of the tree it filters down. It takes a certain type of character to come through the mire and he's pretty much the guy who's done that.
"He's got a little bit left in his contract so he can't take his foot off the gas yet." But first - that long lunch, with no review necessary.
