Tevez, starting successive Barclays Premier League games for the first time in 11 months, scored a hat-trick and Sergio Aguero also netted a fine double as City moved within touching distance of the summit with a 6-1 win at Carrow Road.
"It is impossible. The title race is finished. It is true," said Mancini. "I think now it's too late for us. I am happy because we started to play like we did in the first half of the season today."
He added: "Tevez scored three goals, and Aguero two. That is their job."
Mancini hauled Tevez off within moments of his third goal, which he celebrated by mimicking a golf swing.
The action could be construed as a dig at the City boss, who criticised Tevez for playing golf during his three-month exile in Argentina, although Mancini claimed after the game that he had not seen the celebration.
Many City fans watching may have wondered where City's title challenge would be now had the former Manchester United player buried the hatchet and returned earlier to help his struggling team-mates, but Mancini said he bore no malice against the 28-year-old.
"Carlos did not play for us for six months but it is only in the last month that we have come off the top of the league," Mancini added. "Everyone makes mistakes. It's important that when you do them you apologise."
Canaries boss Paul Lambert was happy with his team's effort despite the hammering - the biggest of his reign at Norwich.
"I am not going to criticise my team," Lambert said. "We were right in it for 70 minutes of the game and the first two goals were absolute rockets."
Source: PA
Source: PA