Gabriel Jesus came off the bench to score a late winner at Leicester and cement themselves in second spot.
Jamie Vardy had hit the post for Leicester in the first half, but both sides wasted numerous chances before Jesus slotted home with a cool finish after a surging run from Riyad Mahrez had opened up the home defence.
The best of those opportunities saw Foxes keeper Kasper Schmeichel deny Sergio Aguero from the spot on the hour mark as the Blues’ penalty problems continued.
The defending champions are now seven points clear of the Foxes having won twice since being banned from European football for two years by Uefa.
“Don’t ask me about the attitude of these guys,” said Guardiola. “You still doubt what they have done. These players have won seven titles in the last eight [domestic] competitions.
“Today, after missing the penalty, see the reaction we had against an incredibly good team, not just for where they are in the table right now but the way they played in general this season. It was an incredible test for us.”
Guardiola’s side have now missed five of their seven Premier League spot-kicks this season, but Leicester will argue they should have been given two of their own before the break.
Nothing was given when Kevin de Bruyne had his arms up in the wall and James Maddison’s free-kick clearly hit them, and even more mystifying was the decision to give Leicester a corner when Ederson took out Kelechi Iheanacho.
Iheanacho had beaten the Brazilian to Maddison’s delightful chipped pass and was floored by the goalkeeper’s attempt to punch the ball to safety, but referee Paul Tierney and the video assistant referee both felt Ederson had touched the ball.
The next time VAR got involved, it was to award the visitors a penalty – after Dennis Praet charged down Ilkay Gundogan’s effort with his arm.
But Schmeichel preserved parity when he saved with his legs after Aguero went for power and blasted his spot-kick down the middle, leaving the game in the balance.
The Foxes keeper denied Aguero again soon after, but he could do nothing to keep out Jesus’ strike which brought a jubilant reaction from the away fans, and the Manchester City players joined them in celebration at the final whistle.