"They are a very good team with very good players, so you have to be on your toes all the time and can't relax for a second".
Cristiano Ronaldo's volley left the footballing world open-mouthed, but it was Juventus that ended Wednesday night stunned as United dug deep to secure a late 2-1 comeback victory in the Champions League.
Guardiola also played down talk that United are not the force they once were, citing their impressive results recently as a reason to not to underestimate the threat they still pose.
"When you win, you are more optimistic in your preparations for the next game", Herrera told the British media. "We have to control the ball more and be clinical".
Against an unbeaten Old Lady side who had only dropped points to Genoa at home this season, United hassled, harried, and looked as if they had a coherent game plan.
"Like all the games are so tight, last minutes no team controlled the game and you have to defend well and try to attack like we've done in the last few games".
"They are a big club, with big mentality, they showed it against Newcastle. We can't talk about luck because everyone makes their own luck but we gave them the victory".
Whatever United's plans, they must involve what has been a problem for most Etihad visitors though, and that is staying in the game. In November, there are five or six strong teams.