Alli struck his side's second at White Hart Lane after City defender Aleksandar Kolarov put through his own net.
Spurs' 2-0 victory margin could have been greater had Erik Lamela not seen his second-half penalty saved by visiting goalkeeper Claudio Bravo but England midfielder Alli knows they ensured the Premier League would sit up and notice.
"It's massive," he told Sky Sports 1
"It was a big statement for us
We know what we were capable of and we knew there were going to be chances if we stuck to the game plan and when they came along we took them."
Guardiola had a perfect record in the league since taking over at the Etihad Stadium but his first defeat leaves them just a point clear of Tottenham at the top of the table, with Liverpool a further point back in third.
City had failed to win for the first time under the Spaniard in midweek as they drew 3-3 against Celtic in the Champions League.
And in London on Sunday they came unstuck against Spurs' pressing game.
Alli added: "I don't think there's any denying they are a brilliant football team and they do like to play the ball
We knew that if we got in their faces and kept working hard that we'd create chances.
"They're a great team and they're going to be up there at the end of the season but I think we showed what we were capable of."
Spurs are now the only unbeaten team in the Premier League and Alli wants to see that run continue after the international break.
He said: "Nobody wants to have that week off without the win so it was massive for us and it was important we keep going, keep fighting and just focus on the next game."
Source : PA
Source: PA