The 37-year-old this week claimed to be the best player in Major League Soccer, and few can argue after this display.
Carlos Vela is the league's top scorer and he opened the scoring from the penalty spot in the fourth minute.
But Ibrahimovic equalised shortly afterwards with a stunning strike, controlling a long pass before lobbing the ball over the head of Eduard Atuesta and volleying the ball past goalkeeper Tyler Miller.
The Swede headed in a Diego Polenta cross after 56 minutes and rifled in a left-foot shot with 20 minutes to play to complete his treble.
Former Arsenal striker Vela scored his second deep into stoppage time to take his tally for the season to 21, but Galaxy held on.