Defensive woes frustrate Guardiola after derby defeat
Guardiola's men appeared on course to be crowned Premier League champions with a record six games to spare when they eased into a 2-0 half-time lead through Vincent Kompany and Ilkay Gundogan.
United stormed back in the second half, though, as a Paul Pogba brace pulled them level and then an unmarked Chris Smalling volleyed in from a free-kick to spoil City's title party.
"We have to be better and more focused on set-pieces," Guardiola told Sky Sports.
"Our team tried to create and attack, that is what we have done all season, we tried to produce all of that quality and goals. You have to defend a little better in the second half, but it is football."
Guardiola's attention will now turn to picking his players up for Tuesday's Champions League quarter-final second leg against Liverpool, where they are faced with the daunting task of overturning a three-goal deficit.
"We will try to pick ourselves up for Liverpool, we are professionals," he told BBC Radio 5 live.
"We were not good enough in the end. The schedule is like this, that's why this competition is so tough."
FT | 2-3 #cityvutd #mancity
A tale of two halves as City lose the 176th Manchester Derby. pic.twitter.com/4fKFBhMoID
— Manchester City (@ManCity) April 7, 2018