City, basking in a sheen of invincibility, went on to claim the Premier League title with a record 100 points from their 38 games.
A year later, City are in a dogfight for supremacy, fighting it out with Liverpool and Tottenham Hotspur.
On Wednesday, City could reclaim pole position from Liverpool for the first time since 8 December 2018 if they are victorious over ninth placed Everton at Goodison Park.
A win will give City 62 points after 26 games and put them ahead of Liverpool on goal difference. The Merseysiders will recapture the lead with a draw or win against Bournemouth at Anfield on 9 February.
"Three or four days ago, we were already done," said Guardiola, on the eve of the game against Everton. "And the champions were Liverpool. Now we are the favourites.
"There will be surprises and it will be tough for teams to win every game. The contenders and the non-contenders have the ability and skills to create problems."
The race has opened up following Liverpool's successive draws against Leicester City and West Ham United.
"What's not common is what happened last season, where we won 18 games in a row and finished with 100 points and a lot of distance ahead of the team in second place," said Guardiola.
"Normal is what happens now, where every game is tough and you can win or lose every single game, because every team is either involved in the title, or Europe, or in trying to stay in the Premier League."
Everton under pressure
Marco Silva, the Everton boss, is under pressure after his side's poor run of form.
Since their 1-0 success over Cardiff on 24 November 2018, Everton have only won three of their 12 Premier League games. There have been seven defeats and two draws, as well as a humbling FA Cup fourth round exit at second division Millwall.
"Every mistake we make at the moment is damaging us," said Silva. "Teams don't need to do something special to get something from us. We are making it easy for them. It will be tough against City but they are not invincible."
How times change.