It was the third treble of the Argentina striker's career at Eastlands and came on his 27th birthday.
Tevez, who conveerted two penalties, 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.
"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."