Matawalu’s three tries came as he was sprung from the bench after an early injury to full-back Ruaridh Jackson at the Liberty Stadium.
The 29-year-old did not take long to get going, registering his first score less than 10 minutes after entering the pitch.
Matawalu swept round DTH van der Merwe as he took a tackle but managed to offload, with the Fijian dotting down after 11 minutes.
Three minutes later Matawalu notched arguably the best of his three efforts.
Nick Grigg showed power to break a tackle and managed to stay on his feet before handing the ball on to his team mate to register his second score on 14 minutes.
Matawalu rounded off his stellar display shortly after half-time. He collected fly-half Brandon Thomson’s wondrous cross-field kick to complete his hat-trick and one of the performances of the season so far.