The top-flight crown was on the line at the Etihad Stadium on Saturday, with three points all the leaders needed to get their hands on more major silverware.
A 2-0 half-time lead suggested that the champagne could be put on ice, but a thrilling fightback from the Red Devils saw them claim a remarkable 3-2 victory and delay the title party.
Guardiola’s side should still go on to claim the trophy, and the Catalan coach feels the odd bump along the way only serves to highlight how difficult it is to secure domestic dominance.
He said in the aftermath of a frustrating afternoon on home soil: "For the fans it is tough and maybe we are going to get more credit if we are able to win the Premier League and people will say how tough it is to win.
"In November, December everybody said the Premier League is done. But it was a tough, tough fight to keep going every weekend to be focused. This is the first time we lost two games in a row.
"Of course we are sad for ourselves, for our fans - but we still have 13 points advantage and goal difference.
"We have to win two more games and after the game on Tuesday we are going to focus on the Premier League to try as quick as possible to get it."
There appeared to be no hangover early on, but the challenge facing Guardiola now is lifting his troops for the return date of a continental clash which has plenty riding on it.
"My dream is that, as in the first half when we didn't concede anything, it would happen again in the second half," he added on City’s unravelling against United.
"But a good manager [Jose Mourinho] maybe said in the first half 'guys, we have to do something more'.
"We were not good enough in the end. The schedule is like this, that's why this competition is so tough. We will try to pick ourselves up for Liverpool, we are professionals."