Matheus Nunes struck a dramatic winner in the fourth minute of added time on Tuesday night at the Etihad Stadium, where Bernardo Silva's early opener for City had been swiftly cancelled out by Marcus Rashford's penalty.
The result saw City (61 points) move up two places in the Premier League table to third with four games to play, with Unai Enery's Villa left two points outside the top five in seventh.
Asked how big a win it had been, Guardiola - whose side face Nottingham Forest in the FA Cup semi-finals on Sunday, a day after Villa play Crystal Palace in the other last-four tie - told a press conference: "If we win the next four games, it has been so important.
"Of course, it's important. We don't have to be a scientist to realise that we play against Aston Villa, one of the best teams. We saw the games against Newcastle and (Paris St Germain), the top form, the quality, the manager, everything. It's an extraordinary team.
"But we performed like we were in the past, the commitment, we concede not much. We didn't create much either, but we controlled most of the game. The back four, again, had been amazing. All the players.
"In terms of qualification for the Champions League, for the points, it's important. But at the same time, we have to be calm and focus on the semi-final, and after, we have days to prepare the four 'finals' - two games are home, two away, and game by game."
In the build-up to the game, Guardiola had referred to the remaining five league matches as "finals", with City to follow the Villa game by hosting Wolves and Bournemouth either side of playing at Southampton, before concluding their top-flight campaign at Fulham.
 It was a blow for Aston Villa's hopes of again featuring in Europe's top club competition but Emery said he would not be dwelling too much on his side's late slip.
"We can't waste time, we lost in the last minute of this match but we competed well - we were close to drawing," the Spaniard told Sky Sports.
"We were trying to win the match as well with the subs, but they do the same and they score.
"Over 90 minutes they (City) dominated more, but we played a good competitive match.
"We'll take a lot of positive things and now is a moment to be positive. I'm going to analyse the match and try to get a lot of information from it."
