City struck twice in the final 12 minutes through Gabriel Jesus and a Kevin De Bruyne penalty to beat the 13-time European champions for the first time in their history.
Madrid will also be without captain Sergio Ramos for the second leg after he was sent off late on for bringing down Jesus, but Guardiola is wary of Madrid’s history of comebacks in the Champions League.
“It’s just the first part, it’s not three points. If one team can overcome this situation, for experience, for everything, it is this club, but of course it is a good result,” Guardiola told BT Sport.
“I am so proud of course but it is just the first step, we have another game, it is not over. So be calm, enjoy it, enjoy the moment. Have a good dinner, good regeneration, on Sunday we have a final, keep going in the Premier League and prepare the second game against Madrid.”
Guardiola again sprung a surprise on a big Champions League night with his team selection as Raheem Sterling, Sergio Aguero, David Silva and Fernandinho were left on the bench.
Jesus was deployed in an unfamiliar role wide on the left, but Sterling’s introduction as a second half substitute pushed the Brazilian up front and swung the game in City’s favour.
After Jesus headed in De Bruyne’s cross, Sterling was chopped down by Dani Carvajal inside the area.
“They press so high and the centre-backs can jump, we saw the space we believed was outside. Gabriel is so quick and Riyad (Mahrez) can do it,” added Guardiola.
“In the end we knew for the last 20-30 minutes, Raheem is so fast too. It was good.”
