It was the third treble of the Argentina striker's career at Eastlands and came on his 27th birthday. Tevez has now scored 20 goals in the campaign with City keeping in sight of a Champions League spot after a comfortable 3-0 win.
Platt said: "We pushed players on in the first half. We knew that when we played at the Hawthorns our full-backs played in their half. The manager (Roberto Mancini) reinforced that before the game. We wanted to play in their half when we had the ball."
He added: "We almost had numerical advantage going forward which enabled players like Carlos and David Silva to come off and find little holes. Carlos has also hit the post as well."
Two of Tevez's goals came from the penalty spot to leave West Brom reeling.
The club captain saw a shot come back off the post in the fourth minute before making the breakthrough 13 minutes later with Steven Reid punished for barging Aleksandar Kolarov. Tevez sent Boaz Myhill the wrong way from the penalty spot.
Tevez extended their lead in the 22nd minute after skipping into the area following a one-two with David Silva before finding the corner with his effort.
He then completed his hat-trick in the 36th minute with his second penalty of the game after Jerome Thomas, for reasons only known to himself, handled in the area. Tevez stepped up and this time sent his effort high over Myhill.
That put the game firmly out of West Brom's reach but Platt - hosting the press conference as Mancini had lost his voice - was unhappy they did not kick on.
He said: "We were a bit disappointed at full-time we have not gone on and got more goals and played in a way we did in the first half. We have kept a clean sheet and that is a bonus. It is important for Joe Hart and his defenders. But what really counts is that we secured the three points."