The slick centre from Cole Harbour, N.S., also added an assist to his hat trick, while Martin Frk, with a goal and an assist, Jonathan Drouin, Luca Ciampini and Stephen MacAuley also scored for Halifax. Zachary Fucale made 37 saves to get the win for the Quebec Major Junior Hockey League champions, who got two assists from MacKenzie Weegar.
Troy Rutkowski had two goals for Portland, while Tie Rattie, with a goal and two assists, and Seth Jones also scored. A shaky Mac Carruth allowed seven goals on 35 shots in taking the loss for the Western Hockey League's top team. Derrick Pouliot added three assists.
The game featured three top ranked North American skaters by NHL Central Scouting ahead of next month's draft in Jones, MacKinnon and Drouin and the trio did not disappoint as each contributed offensively.
But the night belonged to MacKinnon.
Ranked as the No. 1 North American skater for the draft in the early part of the season before being overtaken by Jones, MacKinnon put an exclamation point on his performance late in the second period to put the game effectively out of reach. With a goal and an assist already in his back pocket and the Mooseheads up 4-3, the 17-year-old danced around the big Winterhawks defenceman on a Halifax power play at 14:03 and beat Carruth before firing a puck past the beleaguered netminder from behind the Portland goal-line with 1:25 left in the period.
With the teams tied 1-1 after the first, goals came fast and furious in the second. Rutkowski scored on a shot from the point past a screened Fucale after just 39 seconds and Rattie wove through the Halifax defence on a Portland power play before sliding a backhand home at 2:11 for a 3-1 Winterhawks lead.
The two-goal deficit seemed to spark the Mooseheads, who scored in quick succession to knot the game again. Drouin popped a rebound in from the top of the Portland crease at 3:16 before MacKinnon scored his first of the night on a deflection 1:20 later.
After the Winterhawks' Oliver Bjorkstrand chimed a shot off the crossbar behind Fucale about eight minutes into the period, Campini gave Halifax the lead by walking out of the corner and beating Carruth on the power play at 11:17. MacKinnon then went to work offensively on the power play and the penalty kill to effectively seal it.
Rutkowski scored on a Portland man advantage at 1:09 of the third to cut the Halifax lead to 6-4, but MacAulay restored the Mooseheads' three-goal edge with a shot that was deflected by a Portland defender in front of Carruth at 5:33.
It wasn't as easy early on for the Mooseheads as the Winterhawks, who carried the play for much of the first period in outshooting Halifax 16-7, were unlucky to be tied 1-1 heading to the second.
Rattie ripped off a puck off the post for Portland that stayed out five minutes into the game and Fucale was forced to make a couple of big saves for a Halifax team that was a bit scrambly in its own zone.
Despite having the better chances, the Winterhawks trailed 1-0 after MacKinnon wheeled into the offensive zone and found Frk in the slot, who beat Carruth through the five-hole.
Jones evened the score just 55 seconds later by taking a pass from Tyler Wotherspoon off the rush and beating Fucale with a snapshot over the glove.
The Mooseheads take on the host Saskatoon Blades (0-1) on Sunday, while the next game for the Winterhawks goes Monday against the London Knights (1-0).
Halifax was 2 for 6 on the power play, while Portland scored twice on its eight chances.
Notes: Steve Hartley, the son of Calgary Flames coach Bob Hartley, is an assistant with Halifax. ... The crowd of 8,771 at the Credit Union Centre joined in to help the anthem singer after she forgot the words to The Star-Spangled Banner. ... Super Fan Cameron Hughes has attended the first two games of the tournament, whipping up the crowd up during commercial breaks. Hughes was profiled in Sports Illustrated last August. ... The Memorial Cup was first awarded in 1919. The trophy was donated by the Ontario Hockey Association in honour of the soldiers killed in the First World War. After a rededication in 2010, it now recognizes Canadian soldiers killed in any conflict. ... Portland has won two Memorial Cups (1983, 1998). Halifax is looking for its first title.