The burly winger bagged a hat-trick as the Maroons ran in seven tries, including six after halftime, to secure a 44-24 victory over the Blues.
The teams will head to Suncorp Stadium for the game-three decider on July 8.
The most recent Queensland team to savour a victory at the MCG was in 1995, coached by Paul Vautin, with this year's side delivering in front of a record Origin crowd of 91,671.
Cameron Munster put on a play-making masterclass to orchestrate the second-half domination while halves partner Sam Walker was similarly impressive.
Walker was named man of the match, having also been flawless with seven conversions and a penalty.
"I thought we handled a fair bit of adversity in that first half quite well," said Queensland coach Billy Slater.
"There were some things that were out of our control in terms of some changes ... then off the back of that we went out to the second half and really chased our game.
"And we got it right in the first 15-20 minutes of the second half which put us in a really good position."
NSW skipper Isaah Yeo said his team let themselves down after a solid opening 40 minutes.
"Obviously there was an emphasis at the start of the week in making sure we got that start right and I thought we were doing really good in patches there," the lock said.
"I thought we went in really confident at halftime and we just missed the mark.
"Ultimately, they weren't shooting themselves in the foot like we were."
NSW centre Kotoni Staggs produced the game's opening try in the sixth minute then was sin-binned in the second half for a high shot on Kalyn Ponga.
Selwyn scored twice early in the second half with fellow winger Jojo Fifita leaping high to add a third within 11 minutes as Queensland snared a 14-point lead with 25 minutes to play.
That turned around a four-point halftime deficit, the Maroons having been down 12-8 with the Blues finally getting their start right to score through Staggs.
Debutant NSW winger Mark Nawaqanitawase also touched down early and finished with two tries, looking right at home on the Origin stage as he passed a number of early high ball tests.
Queensland did well to keep NSW in check, with both skipper Munster and prop Tino Fa'asuamaleaui tested for a HIA during the first half.
Despite the disruption, Queensland were able to keep NSW scoreless during that time and instead crossed themselves through Trent Loiero.
Rugby convert Nawaqanitawase showed his freakish finishing prowess to bag a second in 59th minute to put NSW back in the hunt at 26-18.
But they lost Staggs to the sin-bin for a high-shot on Kalyn Ponga as the fullback off-loaded to tryscorer Hamiso Tabuai-Fidow, putting a dent in their hopes of a fight-back.
Cobbo then capped the night in the 71st minute, diving over for his third.
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