Guardiola believes City have rediscovered their groove after digging out a crucial victory.
They were frustrated by Forest and bullied by centre-backs Nikola Milenkovic and Murillo to the extent Erling Haaland barely had a sniff.
Gianluigi Donnarumma was wound up by the imperious Milenkovic, while Josko Gvardiol avoided a yellow card for kicking the ball away.
It was not a classic performance but City have won 24 out of the past 27 points available – the blip being a 2-1 defeat at Newcastle in November.
Guardiola said: “It’s more important how you suffer, how you defend, accept you’re not playing good and can be better and be in the game, otherwise there is no chance. That game last season was lost 10 for 10.
“For a long time the team has wanted to do it and it’s the last game of the first leg of the season, so it’s good to finish with an important three points.
“They are three points but a massive three points mainly for the quality of the opposition. Sean Dyche has created a proper team – this team a few months ago were fighting for the Champions League.
“It’s a top side. I know the momentum is not good but it does not change the quality of the side.”
Former City goalkeeper Joe Hart – who won two Premier League titles with the club – also felt it was a crucial victory.
He told TNT Sports: “Look at the way they celebrated – they know they’ve had a tough afternoon. It was an absolute battle but it was a championship-winning performance. When your back’s against the wall you find a way.”
Last season City finished third, 13 points behind leaders Liverpool, having won the previous four titles.
It was a body blow for Guardiola and he revealed heart-to-heart talks with the squad during the Club World Cup in the summer re-established their focus.
“The critical moment changed in the USA at the Club World Cup. We looked at ourselves and talked and many things changed from there,” he said.
“Now it is a process. When we won a lot of titles at Barcelona, Bayern Munich and here, you had a lot of games of this type.
“The body language, the connection of how we are with the fans – they love the keepers, the strikers, the people, because they feel the team wants to do it, want to fight for each other.
“The fans accept playing badly, but if you don’t put the heart and your commitment for the people who adore the club more than we love it…”