Linus Ullmark made 28 saves for Boston (32-5-4), which was shut out for the first time this season and had a 14-game point streak end (11-0-3). The Bruins had been 19-0-3 at home. It was their first home loss in regulation in 29 games (26-0-3, including Stanley Cup Playoffs) since a 3-2 loss to the Ottawa Senators on April 14 of last season.
"We weren't a second late, we were two seconds late on everything," Boston coach Jim Montgomery said. "We just couldn't see the plays that were there to be made all night. We're not happy with how we played."
The Bruins were coming off a three-game West Coast road trip when they outscored the opposition 16-5 and went 3-0-0.
"I think it just took us a while to get to our game, if it even got there," Boston defenseman Charlie McAvoy said. "They came in and played well, but we just didn't do enough for 60 minutes."
The Kraken have won the first six of a seven-game trip that ends against the Chicago Blackhawks on Saturday. They became the seventh team in NHL history to win each of its first six or more games of a road trip. The last one to do so was the San Jose Sharks from Nov. 13-22, 2015.
Seattle is 15-4-2 on the road.
"It's been fun," Kraken forward Jordan Eberle said. "This has been a long road trip; it's made it a lot easier when we've swept it so far. We're a close-knit group, we have fun together, we win together, and I don't think there's really anyone in that locker room that really cares about the acknowledgement. It's just a team mentality."
Tanev gave Seattle a 1-0 lead at 7:14 of the first period, scoring on a tip-in from a sharp angle after Daniel Sprong shot from the right boards.
"I was hoping for the best," Tanev said. "I know [Sprong is] a great shooter, so you can just park yourself in front of the net and hopefully you can deflect one in, and I was fortunate enough for that to happen."