A breathtaking first-half performance yielded a solitary goal against Liverpool and Jurgen Klopp's men picked off their opponents for a 2-1 win in Manchester and a 5-1 aggregate triumph, the damage City sustained at Anfield last week proving too great to overcome.
City were dominant in the first half and thought they had scored a second goal before the break through Leroy Sane, only for the effort to be disallowed for offside, despite Liverpool'sJames Milner having touched the ball into the German's path.
City also had penalty shouts when Milner blocked a shot with his arm and Raheem Sterling went down under a challenge from Andrew Robertson. Guardiola also pointed to Salah's opener last week, which he claimed was offside, as another crucial decision that caused City to be eliminated, as well as two other key decisions he believed were wrong in that match. "It was the difference between going in at half-time 1-0 and 2-0". I don't think three will easy for them but we need to be ready and a goal is always a good idea.
But the City manager felt it could have been a different outcome if decisions from the officials had gone his team's way in both matches.
Details of the "improper conduct" were not specified, though television pictures showed Guardiola appearing to send communications to his coaching staff from his second-half seat high in the main stand.
Roma legend Giuseppe Giannini has told the Italian media he hopes his former club are drawn against Liverpool in the next round of the Champions League. But I know him [Lahoz] from Spain, so I could imagine that. I was polite, I was correct. "But Mateu Lahoz is a special guy". So, he's a referee, what he likes to feel different, so it's special.
"When everyone sees a thing, he wants the opposite".
Asked why he was sent off after confronting the referee, Guardiola replied: "I said it [Sane's effort] was a goal".
"We made an outstanding 45 minutes but like last season against Monaco with Aguero, when it is a clear penalty and the same referee, in this competition, the teams are so equal, the impact [of decisions] is so big".
Mohamed Salah's goal calmed Liverpool nerves at the Etihad. "Of course that is an influence", he continued.
Klopp has guided Liverpool to the Champions League semifinals for the first time since the 2007-08 season. "They are a top team and a top manager".
Roberto Firmino tucked into a winning breakfast on Wednesday morning after helping seal Liverpool's progression to the Champions League semi-finals in style.
It has been a hard week for City, with their two losses to Liverpool coming either side of a derby defeat by Manchester United.