Messi, whom Guardiola managed at Barcelona for four years, appeared to be having a quiet night after opening the scoring early on 11 days ago, at times seemingly just strolling around the pitch.
But the FIFA World Player of the Year had lulled City into a false sense of security with what Guardiola describes as his "X-ray" awareness, and he ended up scoring a hat-trick in a 4-0 victory for the Spanish champions.
Guardiola thinks Messi is most dangerous when he is standing still and has warned his City players to take heed ahead of the return match at the Etihad Stadium on Tuesday night.
"Messi spends the match making a mental X-ray of every space, every moment," said Guardiola
"It looks like he's walking
It seems like he is alone - detached
Or when he sees the defenders are watching him, he will wander off into a space of his own
"It looks like he's just ambling around and maybe he's the guy who runs least in the Spanish league but, boy, when that ball reaches him he knows the complete time-space X-ray of who is where
Then..
pow!"
After picking up only one point from their last two Champions League games away at Celtic and Barcelona, City need a positive result on Tuesday with only the top two teams in the group progressing to the knock-out stages
Borussia Monchengladbach could leapfrog Guardiola's side into second spot if they beat Celtic at home and City still have to go to Germany.
Guardiola made the surprise decision to leave out Sergio Aguero in the Nou Camp - for tactical reasons.
The striker underlined his importance to the City team with a terrific display, and two goals, in the 4-0 win at West Brom on Saturday and Guardiola revealed the Argentina international will start against Barcelona this time.
"I think so
But I'm not going to tell you in which position he's going to play!" joked Guardiola, who then went on to explain why Aguero did not start in Spain
"I have already said I thought to play one more man in the middle
I wanted more control and I decided I wanted players to arrive in the box, not stay in the box, that's the reason why
I t was a tactical decision."
West Brom boss Tony Pulis felt his players suffered from an inferiority complex against City on Saturday and plans to address the problem with his players ahead of next week's trip to face Premier League champions Leicester
"You try to convince the players they are good enough to be on there (with City)," said Pulis
"Obviously the team sheet comes through and you see the players City have got and they're fantastic players
But you've still got to be up for it and in their faces
"I'll have a good chat with them b ecause it's the third time it has happened against the bigger clubs."
Source : PA
Source: PA