Selecao were without Joao Cancelo who tested positive for COVID-19 and was replaced by Nelson Semedo at right-back while Ronaldo spearheaded the attack, supported by Diogo Jota, Bernardo Silva and Bruno Fernandes.
Portugal had a quick start as Jota came close to giving them a perfect start in the fifth minute after breaking away unamrked on the edge of the box but his thumping effort was parried away by shot-stopper Peter Gulacsi.
Fernando Santos' charges were gaining momentum after that and Jota had another chance to break the deadlock just before the half-hour mark after a through ball by Ronaldo inside the box but Willi Orban made a crucial tackle to deny him a clear sight of goal.
Hungary were struggling to get out of their own half and Ronaldo should have given Portugal the lead just before the break after a cross by Jota found him unmarked in the box but his first-time side-footed shot blazed over the bar.
Portugal picked up from where they left off in the first half, as Pepe almost broke the deadlock two minutes from the break with a header at the back post that saved by Gulacsi at full stretch, from a corner.
Szabolcs Schon thought he had put Hungary ahead two minutes after coming on in the last ten minutes, after going through on goal, cut inside and unleashed a left-footed strike past goalkeeper Rui Patricio at the near post but the goal was disallowed for offside.
The game turned on it's head after that, as Raphael Guerreiro broke the deadlock for Portugal six minutes before time with a strike inside the six-yard box that took a huge deflection and wrong-footed Gulacsi.
A Selecao had a big chance to seal the deal after they were awarded a penalty three minutes before time after Orban brought down Rafa Silva inside the box, with Ronaldo making no mistake to became the all time leading goal-scorer in the Euros with ten goals.
Ronaldo made it 3-0 for Portugal andd extended his record tally at the Euros to 11 goals in stoppage time after rounding Gulacsi from a through ball to score into an empty net, as the reigning champions had a perfect start in Group F.