The South Korean marked his first involvement in pre-season with a standout display, taking just 11 minutes to break the deadlock.
Son returned the favour just three minutes as Lucas headed home from a corner after Eric Dier had twice been denied.
Young centre-back Maksim Paskotsi was being little troubled at the back so looked further ahead to send Son running down the right. The forward looked up and spotted Dele Alli darting into the area for a third before the break.
Dane Scarlett and Nile John, replacing Son and Oliver Skipp, were among the half-time introductions and both almost scored within minutes of coming on.
Dele found John in space on the edge of the area for a shot, which was deflected narrowly wide, before Paskotsi again ventured forward to send Scarlett through on goal and score only to be flagged offside.
A rare Colchester attack on the hour mark saw Luke Chambers forced Alfie Whiteman into a fine save onto the crossbar.
Spurs played out the final minutes with little trouble to record a first win of pre-season.