FIFA World Cup Play-Off: Sweden 2 Portugal 3
Ronaldo had scored the only goal of the first leg in Lisbon on Friday night and it looked to be plain sailing for Portugal when he opened the scoring in the second leg just after half-time.
However, this had been billed as duel between Zlatan Ibrahimovic and Ronaldo and the Sweden skipper stepped up to the plate with a double to level the tie on aggregate at 2-2.
Portugal were still in front on away goals and Ronaldo made sure as he first levelled on the night and then scored his hat-trick to take his tally to 13 goals in his last six games and become his country's joint-leading scorer in the 4-2 aggregate win.
Such was Ronaldo's brilliance that Ibrahimovic applauded the Real Madrid striker when he scored his second goal as Portugal qualified for a fourth consecutive World Cup finals, while Sweden miss out for a second successive finals.
Portugal lost striker Helder Postiga to injury in the warm-up and so Hugo Almeida replaced the Valencia striker, while Sweden coach Erik Hamren kept faith with the same side that was beaten in Lisbon on Friday night.
After a frantic start it was Portugal who came close to the opening goal after 15 minutes, when Bruno Alves rose to meet Jose Moutinho's inviting free-kick and his downward header was palmed away by Andreas Isaksson.
Ronaldo tried his luck with his left foot from 25 yards 10 minutes before the break, but Isaksson got down to make the save. And the Real Madrid forward should have done better less than a minute later when he blazed over the crossbar from around 12 yards out after Joao Pereira picked him out.
Sweden were struggling to live with the Portugal captain's movement and seven minutes before half-time he found space then stood up a cross to the back post for Almeida, but the Besiktas striker headed wastefully wide of the near post from close range.
Ronaldo had yet another chance two minutes before the break when he got on the end of Nani's cross but once again failed to test Isaksson.
Sebastian Larsson had a golden opportunity to put level the tie three minutes into the second half when Rui Patricio denied him from 10 yards out after Ibrahimovic had pulled the ball back.
And that miss proved costly, as just a minute later Moutinho set Ronaldo away with a delightful throughball and this time he made no mistake with a deadly left-foot finish to stun a partisan crowd.
Sweden looked devoid of ideas, but they were given a lifeline after 67 minutes when Ibrahimovic headed home a corner from the right.
The Swedes thought they had a penalty soon after when Kim Kallstrom tumbled in the area, but referee Howard Webb booked the midfielder for diving.
Ibrahimovic took things into his own hands once again, however, when he rifled a free-kick through the wall 18 minutes from time to level the tie on aggregate.
Ronaldo was not finished yet, though, and he levelled with a fine left-foot finish as Sweden were hit on the break 13 minutes from time and then completed his hat-trick a minute later by rounding the keeper and netting once again.
There was still time for Ronaldo to almost become Portugal's leading scorer, but this time he was narrowly off target. However, that was never going to take the gloss off his outstanding display.