Wembley Stadium — and a first appearance in the final since 1976 — couldn't be any closer for free-scoring City after an embarrassingly one-sided contest that also featured two goals from Edin Dzeko and another by Yaya Toure.
The result heaped further humiliation on West Ham and its under-fire manager Sam Allardyce, who saw his relegation-threatened side lose 5-0 at second-tier Nottingham Forest in the FA Cup on Sunday.
"It's not unique to us is it?" Allardyce said. "Manchester City have done this to Tottenham and Manchester United. We knew they had to have an off night and they didn't."
Sunderland beat Manchester United 2-1 on Tuesday in the first leg of the other semifinal. The second legs are in two weeks' time.
Allardyce had fielded a shadow side full of kids and fringe squad members against Forest to ensure his main players were fully recharged for this match. It proved to be a complete waste of time.
They were steamrollered by a City team that took its goal tally at the Etihad this season to 59 in 15 games. At times, it was embarrassing and downright cruel as the hosts toyed with their opponents, with Negredo moving onto 18 for the season in his first year at City.
"Playing better than the way he did today is not easy," Pellegrini said of Negredo. "He really played a complete game."
City was everything United wasn't against Sunderland: sharp, full of movement and unforgiving in front of goal. The gap between the two Manchester rivals hasn't been so great in a generation.
Negredo and Toure were at the heart of everything for City and they combined beautifully for the first goal in the 12th minute. Toure floated a long pass through the middle of West Ham's open defence, the ball dropping over the shoulder of Negredo who buried a first-time volley into the corner.
The Spain striker made it 2-0 in the 26th by sprinting onto Dzeko's reverse pass and delivering a finish on the slide, and Toure inflicted more punishment just before halftime, running from halfway toward back-pedaling defender Roger Johnson and calmly stroking a shot low into the centre of the goal.
Johnson was signed from third-tier Wolverhampton Wanderers on Monday to ease West Ham's defensive injury crisis that has deprived Allardyce of all his centre backs. He couldn't have endured a more miserable debut.
The misery was far from over for West Ham, either.
Negredo completed his second hat trick for City with a snapshot in the 49th after David Silva's low cross deflected into his path and strike partner Dzeko got in on the act on the hour mark, poking home a near-post finish from Gael Clichy's centre.
As Allardyce looked on gloomily from the technical area as the rain poured down, Dzeko added the sixth in the 89th with a vicious left-footed shot into the top corner. Allardyce was given a vote of confidence from West Ham's co-chairmen after the Forest defeat but he looked a beaten man here.
"However hard they tried, and they did, was not good enough to stop the quality and talents Man City have bought on the finance that is available to them," Allardyce said.
City has won all 12 of its home games in domestic competition this season and scored 92 goals in 31 games in all competitions.
"We have not arrived in the final but we are very near," Pellegrini said. "It is very important to continue in all the competitions playing the way we did today."