The Citizens made hard work of the fixture against the Football League two side, with an early own goal given them the lead but had to wait until the 85th minute to get their second through substitute Marc Guéhi.
The Premier League outfit also
"We didn't read the spaces where they were," said Guardiola after the match.
"Always the spaces we attack depends on where the defend and we didn't read it. We have to spend a lot of time to make the process quicker and better. The only good news is we go through."
The match marked Man City's 14th fixture since the start of 2026, with the club battling for the Premier League, UEFA Champions League, FA Cup and next month's Carabao Cup final against Arsenal.
"Would be nice to say that mentally we're exhausted but this is our job and we have to do what we have to do," added the Spanish coach.
"We didn't read the spaces, that's why everything was flat and slow, and it was not good. It has been tough but not just these two weeks, since November it’s been every three days and that's a lot."
Pep Guardiola's side will have a bit of rest before taking on Newcastle United in a Premier League encounter at the Etihad next Saturday.
Newcastle United staged a thrilling turnaround to defeat 10-man Aston Villa 3-1 and secure their place in the fifth round of the FA Cup, with Sandro Tonali's double proving decisive.
Arsenal captain Martin Odegaard wants his team to do better in the FA Cup this season ahead of the fourth-round tie against Wigan Athletic at Emirates Stadium on Sunday.
Liverpool advanced to the next round of the FA Cup after defeating Brighton and Hove Albion 3-0 in their fourth-round clash at Anfield on Saturday evening.
Newcastle United overturned an early deficit to beat Aston Villa 3-1 in an FA Cup fourth-round tie marred by refereeing controversies.
