The cheering was still reverberating at the Ashton Gate home of the second tier Championship club on Wednesday after their last-gasp 2-1 quarter-final win over the Premier League giants when the semi-final draw offered them an even giddier follow-up.
For the Robins’ reward on one of the finest nights in their 123-year history was to set up the prospect of another when Guardiola’s Manchester City, Europe’s team of the moment, visit them in a last four, second leg tie in January.
Johnson was asked how it felt to be presented with the hardest task in English football against a side unbeaten in domestic matches this term.
“It’s brilliant,” he enthused.
“We move on now. We didn’t show United too much respect. Now it’s on to Manchester City over two legs and there’s another chance for the players to test themselves against another elite group,” he said. “City are a beast of an organisation.”
The beasts who have been devouring all Premier League opposition this season, though, may find Ashton Gate as tricky and oppressive a venue as Mourinho’s men, who became the Robins’ fourth Premier League victims of their inspired Cup run.
The key will be managing to stay in the tie in a testing first leg at Man City’s Etihad Stadium early in the New Year.
If they can keep any away-day deficit down to manageable proportions, Johnson’s young, eager outfit could cause a few problems in the return at their tight Bristol fortress.
The exultant scenes that greeted Korey Smith’s 93rd minute winner would, reckoned Johnson, “live in the memory of this football club for many years.”
His father Gary was one of City’s more successful managers when Lee was a player at the club. “But I think tonight was the greatest moment in both of our tenures,” reckoned Johnson, whose team are pushing for promotion in third place.
”My dad always says he was the most successful Bristol City manager so maybe I’ve pushed him a little bit close with that result.
“The players have been phenomenal. It’s a young group with real quality and energy and every single one of them will go down in the folklore of Bristol City football club.”
None more so than Joe Bryan, a popular Bristolian and product of the club’s academy, whose wonderful second-half strike had put City ahead before Zlatan Ibrahimovic’s equalising free kick looked likely to inspire a United comeback win.
Still, City kept believing and were rewarded by Smith’s superbly taken left-foot winner on the turn in the final seconds.
Mourinho, while praising City for playing “the game of their lives”, could not quite bring himself to offer unqualified admiration as he kept suggesting the home side were “lucky” to survive with Ibrahimovic and Marcus Rashford hitting the woodwork.
Yet he understood this was City’s night, “a beautiful night for football”, even if he did not have time to hang around and share the special £450 bottle of fine Portuguese wine that Johnson had bought to entertain him.
“Jose was very humble afterwards but he shot off so he couldn’t stay and have some wine,” smiled Johnson. “But I got to ask the questions I wanted.”
And, anyway, who needed wine when this was clearly a night for champagne?