David Silva netted an equaliser on the stroke of half-time for City, who fell behind when Raffael drove home emphatically for the hosts.
The second half became disjointed as Gladbach's Lars Stindl and City's Fernandinho were sent off in quick succession, but Barcelona's victory over Celtic at Parkhead means City are through to the last 16 as runners-up in Group C behind the LaLiga champions.
"The first part of the season, it is so important to qualify for the next round and we did it –now we can focus on the Premier League," said Guardiola on BT Sport, following his latest tussle with a Gladbach outfit that regularly caused Bayern Munich problems during his three seasons in the Bundesliga
"Of course, I was training here in Germany and I know how difficult that team [Gladbach] is.
"But we did it, so big congratulations to the team."
Guardiola felt the strike from his captain Silva was a pivotal moment and refused to comment fully on Fernandinho's second booking for lightly tugging Raffael's shirt - refusing to give full voice to a suspicion that referee Cuneyt Cakir was seeking to even things up after Stindl's clash with Nicolas Otamendi.
"Of course it is better to go to the half-time 1-1 than the other result. It was so, so important that moment, of course," he said.
"The referee, you know after a red from the…oh, it doesn't matter. It doesn't matter."
City began in a 3-2-4-1 formation and Guardiola implemented various tweaks and changes throughout the match, but he rejected the notion that tactical confusion was behind a largely disjointed first-half showing.
"In some moments it is not about the tacticals," he said. "Tactics are so important but the reason why in the first half we didn't play good is another reason.
"The players know that and we are going to work on that."
Top scorer Sergio Aguero was moving gingerly by the final whistle, but Guardiola does not envisage him being an injury doubt for Saturday's Premier League trip to Burnley at this stage.
"Maybe he had a kick but he's okay," he added.