City, held to a 1-1 home draw by Middlesbrough on Saturday, have won one of their last five Premier League recreations to slip to third in the table behind Liverpool and Chelsea.
“Now and then when you miss a point it’s a disgrace… we’re assaulting with 10 folks and we don’t give (rivals) a chance to run,” Guardiola told journalists.
“We have to insist on playing that way but we have to be better in the boxes. When that happens the game will be 2-0 and the game will be over.”
Having taken a first-half lead through Sergio Aguero against Middlesbrough, City dominated possession, but spurned chances to make the game safe before Marten de Roon’s stoppage-time header condemned the hosts to their third consecutive league draw at the Etihad Stadium.
“We control the attack, outside and inside the box and we get to the second balls,” Guardiola said.
“Of course, in 90 minutes, there has to be some point when the opponent can arrive in your box and what happens here is that they punish you,” the Spaniard added.
“Here, the games are always open because they put the long balls on to the strikers. They are playing for free kicks and throw-ins to make the most of the minimal mistake.”