With just seven minutes gone, England won a corner down the right, with Tottenham's Kieran Trippier heading forward to swing it in.
The delivery was perfect, allowing Cahill to rise and power a header beyond Francis Uzoho in the visiting goal and the man on the post to open the scoring.
Remarkably, Cahill is the fifth-top scorer in England's World Cup squad, with five international goals.
The goal was England's earliest strike at Wembley since Wayne Rooney scored after six minutes against Lithuania in March 2015.
June 2, 2018