The Edmonton native was just one point shy of a WHL playoff record for points in a game, but doesn't want to celebrate his achievement with so much post-season hockey to still play.
"I don't think I've ever had a night like that ... but it's one game and I'm going to move on," said Legault. "I feel like anywhere I play I can contribute. Tonight I was the beneficiary of playing with two good players who also had good nights."
Trevor Cheek had two goals and an assist for the Oil Kings while Michael St. Croix scored once and set up two others.
Cody Corbett, Keegan Lowe and Travis Ewanyk each scored once for Edmonton and Martin Gernat chipped in with three assists.
Laurent Brossoit stopped all 28 shots he faced for his third-career post-season shutout.
Jagger Dirk and Austin Vetterl were both minus-4 for the Ice.
"We got outclassed by a championship hockey team," said Kootenay head coach Ryan McGill. "Certainly we need to be better on Sunday, and take a long hard look in the mirror at our individual preparation. We need to understand we're playing for keeps ... we don't have time to wade in."
Mackenzie Skapski took the loss after allowing five goals on 15 shots in the first 20 minutes of play. Wyatt Hoflin replaced Skapski to start the second period and stopped 20-of-24 shots in relief.
"I think he was a bit nervous but we weren't very good in front of him to take away second and third opportunities," said McGill of netminder Skapski. "We have to be way more disciplined."
Edmonton went 3 for 7 on the power play while Kootenay failed to score on five chances with the man advantage.
Legault opened scoring after deflecting Gernat's point shot behind Skapski at 8:26 of the first period. Just 1:40 later, Legault blasted a cross-ice pass into the open cage before Ewanyk caught Skapski leaning off the post at 11:23 to put the Oil Kings up by three.
Legault polished off the hat trick at 16:30 on the power play, beating Skapski through the legs off the left wing.
Cheek sent Edmonton into the second period with a 5-0 lead, stretching out with 18 seconds left in the first to whip the puck in off the post from inside the faceoff circle.
With Hoflin starting the second period between the pipes for Kootenay, St. Croix scored his first of the playoffs at 3:03 with a spinning backhand in a scramble.
Corbett struck on a two-man advantage at 9:24, stepping in off the point to wire a wrist shot into the glove-side corner and Lowe wired a one-timer behind Hoflin at 16:44 on the power play for an 8-0 lead.
Cheek added his second of the game to finish off the scoring, tapping in a rebound at 5:36 of the third period.
The Oil Kings lead the series 1-0 and will host Game 2 on Sunday at Rexall Place.
Alfie Turcotte and Dave Chartier share the WHL single-game playoff point record with eight. Turcotte did it in 1983 with the Portland Winter Hawks while Chartier recorded eight points in 1983 as a member of the Brandon Wheat Kings.