The goal came midway through an exhilarating overtime.
It's the eighth gold for the Americans in the last ten Women's Worlds but the first ever on home ice. Canada has not won gold now since 2012 in Burlington, Vermont.
Knight also scored the overtime winner in 2011 in Switzerland.
"The last time we played at home we lost to them in Vermont, and we didn't want that feeling again," said defenceman Kacey Bellamy, who scored the Americans' two goals in regulation. "The support we've had the last few weeks has been incredible, so we wanted to win this for the fans."
"I was just thinking, 'I have to block this shot,' and then I was thinking, 'I have to get it to Kendall,' because she's fast as hell," Knight described. "She created a lot of separation for me, so I just kind of filled in behind her and took the shot."
"She got the puck up to me and I just rushed in with speed," Coyne said. "I knew Hil was right behind me. When you have the best player in the world behind you, you get her the puck."
The 5-on-5 overtime period was nothing short of heart-pounding. Canada killed an early penalty and made a goal-line clearing earlier, and had its own chances to score, but in the end it was a mistake at one end and a great shot at the other that won the game.
"We're both great teams," Knight continued. "You have to try to cut the odds in your favour, but at the end of the day you saw a great hockey game."
Has there ever been a faster women's hockey game than that played tonight in Plymouth? The Americans and Canadians tore up and down the ice all night long. USA Hockey arena was packed, and it pretty evenly represented the two nations as chants of "USA! USA" were offset by "Go, Canada, go!"
"I heard the Canada chants, and then was thinking, 'Come on! Let's get the U.S. chants!' It was an awesome atmosphere," Knight added. "To get the fan support was amazing. We often play in places we're getting booed, so cheers were great."
"I thought we played really well," offered Canada's Meghan Agosta. "I think the biggest thing we can take out of this is to get more quality shots on net. It's tough right now, but we need to bounce back."
Canada scored just 61 seconds after the opening faceoff when Jennifer Wakefield collected a loose puck in her end. At that moment, Agosta tore up ice, and Wakefield fed her as they skated in over the blue line on a 2-on-1. Agosta ripped a wicked shot over the glove of Nicole Hensley to stake Canada to an early 1-0 lead.
The goal assuredly woke up the Americans, who won the first meeting a week ago by an impressive 2-0 score. Canada might have added to its tally on a power play soon after, but soon after the hosts tied the game.
A faceoff win in the Canada zone got the puck back to Kacey Bellamy, and her hard shot was screened, making its way into the goal without Shannon Szabados having much of a chance on it. That goal came at 4:34, and both teams were now fully into what was clearly going to be another battle.
The period was back and forth, up and down, the Americans having the better chances, but Szabados steady all the while. Canada's Natalie Spooner made a great rush alone against two defencemen in the final minute, but her shot rang off the far post and it remained a 1-1 game through 20 minutes.
The looseness of the opening period wasn't quite there in the second, a period in which Canada had the upper hand. The team was more intense on the puck and pressured the American puck carrier at every touch.
But the goalies were letter perfect, Hensley and Szabados stopping everything shot their way, though the former with far more difficult and plentiful shots. A tie game after two, and the seeming certainty of another one-goal victory either way, seems so common we sometimes take for granted how exciting this rivalry is.
The game took a huge turn in the opening minute of the third when Bellamy snuck down to the top of the crease and knocked in a quick pass from Knight just 42 seconds in. After that, the Americans swamped Canada, but they couldn't get that third goal.
Resilient Canada finally tied the game on the power play. Poulin drove down the right wing and got the puck in front where Brianne Jenner knocked it over the goal line at 9:44.
The game felt like overtime after that, but Canada had to kill off two late penalties to get to a fourth period, which it did expertly. The Americans had plenty of puck movement and several great chances, but Szabados was there to hold the fort.
That set up another dramatic conclusion in extra time.
The Americans are world champions, but once players from both teams return home, they'll all have only one thing on their minds--PyeongChang.