Son, who has struggled for form this season and was left out of the starting lineup by Spurs’ stand-in manager Cristian Stallini, then doubled the advantage by connecting with Harry Kane.
West Ham began the derby with Jarrod Bowen wasting an early chance but offered little and have now won only once in their last 11 league games with pressure mounting on manager David Moyes.
Tottenham have 42 points from 24 matches, one more than Newcastle, who have a game in hand. West Ham are in 18th position with 20 points from 23 matches, one point below safety.