Although Chievo started positively, Juve managed to take an early lead in style through Costa, before Can made it 2-0 late in the half – the Germany international scoring for the first time since joining from Liverpool.
Ronaldo wasted the chance to extend the advantage in the 52nd minute, though there was never any risk of a fightback, as the plummeting Flying Donkeys suffered their 11th defeat of the season to remain nine points adrift of safety, with Rugani wrapping things up late.
Chievo kept Juve at bay for just 13 minutes, as Costa took things into his own hands with a darting run in towards the centre, before drilling a left-footed drive into the bottom-right corner from 30 yards.
Juve stepped things up another notch after a bit of a lull – Stefano Sorrentino making an unorthodox save with his right foot to divert Federico Bernardeschi's deflected 20-yard strike off target.
He was helpless to deny Can just before the break, however, as the German opened his Juve account with a calm finish from just inside the area after an incisive run and pass from Paulo Dybala.
Juve should have extended their lead early in the second half, but Sorrentino produced a fine save to keep Ronaldo's penalty out after a Costa strike had been handled by Mattia Bani.
Sorrentino was eventually beaten for a third time in the 84th minute, however, as Rugani met Bernardeschi's left-wing free-kick delivery to head in.