City won 2-0 in the first leg of their last-16 tie against Borussia Monchengladbach in Budapest, with Bernardo Silva and Gabriel Jesus on target either side of half-time.
Despite watching his team show almost complete domination while racking up a 19th consecutive win in all competitions, Guardiola sometimes cut a frustrated figure on the sidelines at the Puskas Arena.
Speaking to BT Sport after the match, the City boss warned his players not to repeat the mistakes of botched chances that have stained three consecutive quarter-final exits.
"In general, it was good," he said. "We controlled the game, we concede one chance at the end.
"Unfortunately, we were not clinical enough up front – one against one, against the defender and keeper
"It's something we have to improve in this competition.