The 18-year-old made his first Premier League appearance as a second-half substitute in the 8-0 win over the Hornets and impressed with his composure on the ball.
City's backroom staff were unsure whether Watford would line up with a back four or a back five, and it was an eagle-eyed Garcia who accurately identified their plan.
“He played in the Carabao Cup [last season] and was outstanding,” Guardiola said.
“Tuesday he will play against Preston. Incredibly clever guy, able to lead the line.
“With the ball, incredible, knows absolutely everything.
“Pays attention in the warm up. We had doubts about whether Watford would play four or five in the back - and he saw they made some movements in their warm-up that they would play four at the back.
“He’s so clever. Played well. He’s going to play a lot of minutes.”
REPORT | City 8-0 Watford
The French left-back made his first start this season after recovering from a long-term knee problem, before being substituted at half time.
“Mendy is well but after two years playing few minutes, 45 minutes was enough,” he said.
“Angelino is incredible nice guy, training well, deserved to play. I saw many good things of him.
“In the back department, we don't have too many players. We play everyone.”