The 18-year-old German opened the scoring at Landore on 38 minutes but the Welsh side reacted quickly, with Aaron Lewis equalising two minutes later.
The score remained 1-1 until Matondo converted Ian Poveda’s through-ball with 16 minutes remaining.
Jeremie Frimpong added to the lead before Matondo sealed his hat-trick in stoppage time.
The goal sent him joint top of the PL2 scoring chart with six goals alongside team-mate Navili Touaizi.
Everton host West Ham United, while Leicester are at home to Arsenal.
Swansea are 11th on three points.
See: Man City report