The USA looked commanding in the early period of the game and it took the hosts just four minutes to find an opener, as Dempsey met a cross from Timothy Chandler to head beyond a helpless Diosvelis Guerra.
Jurgen Klinsmann's men soon found themselves two goals to the good thanks to some neat attacking play from Gyasi Zardes, who got the run on his marker to get on the end of Alejandro Bedoya's perfectly-timed delivery to tap home.
The host nation had the game all but sealed before the half-time whistle when Omar Gonzalez made it 4-0 on 41 minutes after profiting from some terrible goalkeeping from Guerra, who failed to claim a corner having rushed off his line.
Dempsey was presented with the perfect chance to grab his second goal of the game in the 65th minute after Johansson was brought down in the box, and the striker obliged by sending a clever penalty straight down the middle to make it 5-0.
The former Tottenham Hotspur striker completed his hattrick 13 minutes from time as he slid into the net from a Bradley cut-back to earn his sixth goal of the showpiece.