City played a disappointing 1-1 draw against Boro on Saturday after their impressive 3-1 defeat of Barcelona
City went into the game on the back of a stirring 3-1 victory over Barcelona in mid-week and took a 43rd-minute lead courtesy of Sergio Aguero's 150th goal for the club.
But Marten de Roon's stoppage-time header earned Boro a point and left City vulnerable to attack from the teams below them in the Premier League table.
Asked if City had paid the price for their efforts against his former club Barcelona, Guardiola said: "Not really. We started amazing and played really good in the first half.
"We have to close the game with a second or third goal and we couldn't do that. We created six or seven chances and didn't score."
De Roon's goal condemned City to a third consecutive 1-1 draw in home league games, but Guardiola was phlegmatic about the prospect of his team being overtaken.
"When you miss (opportunities), you have to accept that, but the league is still long," he said.
"It is a miss because we have dropped six points in the last three home games, but we are still there. We have to move forward."
The result extended Boro's unbeaten run to three games following a 0-0 draw at Arsenal and a 2-0 win over Bournemouth.
"It was an amazing result. Because in the first half we went on to the pitch with too much respect for them," said Boro manager Aitor Karanka, who steered the club to promotion from the Championship last season.
"I told them at half-time we weren't just there to defend and that we could play like we did in the second half. I was pleased with our performance.
"Two weeks ago at Arsenal was more difficult than today because Arsenal didn't score and we were organised. Our reaction was really good and it is a big step to showing how good we are."