Costel Pantilimon will look back on this afternoon with fondness, although as an audition to become the new Manchester City No1 this was a nonevent.

By the time Edin Dzeko's late strike consigned Norwich City to a 7-0 humiliation the home team had their biggest win of the Premier League era – and in the top flight since recording the same score against Burnley in 1968 – and the best fillip for Tuesday's Champions League encounter here with CSKA Moscow.

On the day Joe Hart finally heard the executioner's song as Manuel Pellegrini axed him for Pantilimon, the news got better for the 26-year-old after John Ruddy, a prime contender for his England jersey, had a shocker of a first half.

Explaining his decision, City's manager said: "For this game I think that Joe needs a rest, it could be useful for him. He played the last two and a half years every match here, every player can have a bad moment and we will work hard behind Joe so that he can return to his normal best performance as soon as possible."

Pellegrini was vague regarding the time Hart might return. "I don't know. I only know that he must work very hard, he knows he must do it," the Chilean said. "I am sure he will return to his normal performance."

By the time the teams wandered off at the break it was 4-0, the contest felt over, and Ruddy had been at fault for two of those goals while also appearing unsure under the high ball.

With Pantilimon watching from the metaphorical armchair at the other end, Ruddy's opening howler allowed City to go two up. This occurred when the excellent Samir Nasri, who led City's symphonic attacking forays, swept a left foot pass into Sergio Agüero.

The Argentinian, who remains the standout performer at the club, considered the shot. Instead, from the left of Norwich's area, he played the ball to David Silva. The Spaniard let fly but instead of repelling the shot Ruddy allowed it to creep under his body.

While the 27-year-old had not been at fault for City's opener – a Silva shot ricocheted off Russell Martin before Agüero's follow-up took a deflection from Bradley Johnson beyond Ruddy – the goalkeeper was liable for the third.

This arrived on 25 minutes. Nasri floated in a corner from the right that landed on Matija Nastasic's head and though there was a slight bounce off Martin, Ruddy, diving to his left, saw the ball creep under an arm.

At this juncture Pantilimon, on his Premier League debut, probably felt life among the elite was a stroll and Hart might have been found cursing his luck at missing a canter of an outing.

Álvaro Negredo, who would be replaced at the break by Dzeko, added the fourth when Agüero coasted into the area and rolled the ball to his striker partner to slot in.

The prevailing sense now was that City could clock up as many as they wished. By the hour mark the count was 5-0. Yaya Touré continued his new habit of curling a 25-yard free-kick from the left past the opposing goalkeeper. The offering that beat Ruddy in this fashion was his fourth, to follow those against Newcastle United, Hull City and Fulham.

In the first half Pantilimon had actually been called into action. He began this sequence by acquitting himself finely by stretching his 6ft 8in frame to his right to tip Anthony Pilkington's long-range shot wide. But from the ensuing corner Hart's replacement was indecisive as the ball looped in front of him before bouncing to safety.

Yet with Agüero later adding a sixth deep into the second half ahead of Dzeko's finish this was a mere footnote as the focus moves to Tuesday and whether Pellegrini retains Pantilimon.

For Chris Hughton the inquest starts, with Norwich's manager confident he can turn around a side with eight points from 10 games. He said: "I have confidence in my own ability and in the players. We have been in this position before, although not after a defeat like we have had today. We need to put it to bed as quickly as possible and be far better next week. You have to be resilient but you can't concede the goals we did. For our standards they were too soft, except the Yaya Touré free-kick and one that was offside."

What Roy Hodgson, the England manager, made of the unconvincing display from Hughton's No1, as a pretender to Hart, is of material interest in this World Cup season. Despite two sharp saves from Jesús Navas and Martin Demichelis towards the end of the game, for the Norwich keeper, after fluffing his big chance, today had proved an unfortunate case of "Goalkeeping: Ruddy, hell."