Tim Thomas stopped 25 shots to record his first shutout of the season.
With expectations high due to the Maple Leafs hot start, the game was billed as "first vs. worst," but the defending Stanley Cup champions served notice that the road to the Northeast Division title still leads through Beantown.
For the second time this season, Seguin, 19, dominated the Maple Leafs. Seguin scored 3 goals Saturday, and now has 6 points in 2 games versus Toronto this season.
"I was a Leaf fan growing up all my life … I can't lie about that," Seguin said. "To get a hat trick against them is something pretty cool."
Coach Claude Julien noted the rapid development of his second-year star.
"This year he's a confident player," Julien said. "I never doubted his skill level. It was just about him understanding the game at this level, and he understands it very well. He's been arguably our best player since the start of the season."
Seguin's performance overshadowed League-leading scorer Phil Kessel once again, with the second year man getting the best of the player he will forever be linked with through the Leafs-Bruins trade of 2009.
Kessel was held in check by the Bruins team defense, and is pointless in 2 games against his former team this season.
"They played a good game and it showed," Kessel said. "They beat us pretty good."
"We didn't compete right from the opening puck drop and it's pretty disappointing. This was a big game for us. Stanley Cup champs coming in, and they kicked our (butts) every which way."
Seguin opened the scoring on the power play 6:23 into the game on the power play, firing a one-timer past Ben Scrivens off a crisp pass from Rich Peverley. Seguin's sublime skill was on display early in the second period, as he batted in a deflected puck chest-high on the backhand. The Bruins scored again just 8 seconds later, as Lucic beat Scrivens on a breakaway after taking a great feed from Zdeno Chara.
With the two quick goals, the Bruins took control of the game and never looked back.
While the Maple Leafs held the edge in shots through the majority of the second period, they couldn't beat Thomas, who looked sharp. With 5 minutes left in the period, Seguin struck for his third of the game, taking a Patrice Bergeron feed on the rush and beating Scrivens high to the short side. Just 14 seconds later, the Bruins struck again as Scrivens kicked a rebound right to David Krejci in the slot, where he fired it into the open net to make it 5-0. The hook mercifully came for Scrivens in his second NHL start after Krejci's goal, as he was replaced by Jonas Gustavsson.
Lucic scored his second of the game at 5:44 of the third period, off the rush on a feed from Krejci, and Gregory Campbell completed the rout just 28 seconds later when he beat Gustavsson off a scramble in front of the net.
Dion Phaneuf provided the only excitement of the third period with a big open ice hit on Chris Kelly, but the captain's intensity was a lone bright spot for the Maple Leafs on a dismal night.
For the Bruins, nights like this one have been few and far between this season. Thomas knows they can't get complacent after a big win.
"We have to build off this," Thomas said. "(We have) another game Monday (against the Islanders) and we have to focus on that one, get ready to win it and start letting them add up."