City may have won the match but Yokohama, who are currently second in the J-League, put up an impressive fight which saw them have 58% possession against Guardiola's side.
Postecoglou's men created a number of chances, and the style in which they played impressed Sterling.
"They’re probably one of the best teams I’ve seen play out from the back and they played some great football so it was a great test for us," the English superstar said.
Guardiola, who has won 27 trophies as a coach, including two Champions League titles and eight league titles, also voiced his approval of Postecoglou's tactics.
"Yokohama played some incredible football and they were an incredible test for us. I knew how good they were and it was tough for us," Guardiola said.
Kevin De Bruyne opened the scoring for City in the 18th minute, before Yokohama's Keita Endo equalised five minutes later.
Sterling gave City the lead just before half-time and then in injury time youngster Lukas Nmecha sealed the 3-1 win.
City's next game is the FA Community Shield against Liverpool on August 5, while Yokohama resume their J-League campaign against Shimizu S-Pulse on August 3.
