In a good week for English sides in the Champions League, Pep Guardiola and Mauricio Pochettino's side consolidated their place at the top of their respective groups by beating their main challengers.
A Dele Alli double and a goal from Christian Eriksen fired Spurs to a win over the reigning European champions at Wembley and ensures they hold a three-point lead over them at the top of Group H.
Meanwhile, City's came back from a goal down to record a 4-2 win over Napoli in the Stadio San Paolo to maintain their perfect record in the competition.
Guardiola said afterwards that Napoli may be the best side he has ever faced, and Bellamy believes it was their performance which was most impressive.
"It sounds crazy because it's Real Madrid and they haven't lost a group game in five years, but I felt if Man City could go to Naples and win that was a big win,” he said on Sky Sports.
"For me, that was Manchester City's biggest challenge of the season. Of course they've had Chelsea, but look at the form Napoli are in at this present moment.
"Real Madrid are not in great form, but the way Napoli have been playing at this moment, for Man City to go there and win is incredible.
"Napoli are one of the form teams in Europe, a possession-based team.
"I've been really impressed with Napoli. Playing-wise in European football they have really impressed me this year, so that is a really good win.
"That's a really good statement for Pep Guardiola's team."
Spurs star Alli insisted that beating Zinedine Zidane's team was no surprise to him and former Man City star Bellamy believes such results will become a normality for them.
"For Tottenham and where they are looking to go in the next few years, they needed this. But I don't see this being a one-off,” Bellamy added.
"I see Tottenham under Pochettino being here for a while and getting more results like this in the next few years.
"They are here for a long time."