Dallas outshot San Jose 14-6 in the first period.
"I thought [Reimer] was our best player in the first period," Boughner said. "They came out hard. He just looked pretty poised in there all night. I think we fed off of that a little bit and felt comfortable being in a 1-0 game for a long time until we got the second one."
Karlsson made it 2-0 at 16:28 of the second period with a slap shot through traffic, his fifth goal in seven games and 10th point (five goals, five assists) in 10 games.
"He's been a catalyst for our offense really for the last little while, and he and Tommy [Hertl] are taking charge," Boughner said. "He looks calm there. He has that skill of breaking us out of our end and he's shooting the puck a lot better."
The Stars challenged for goalie interference but video review upheld the goal and they were assessed a minor penalty for delay of game.
Raffl cut it to 2-1 at 8:26 of the third period when he redirected a shot by Radek Faksa.
"I thought we played better than we did in those other two games," Raffl said. "That was one of our better games that we've played lately."
Sharks forward Kevin Labanc sustained an upper-body injury 3:02 into the first period when he was hit into the boards by Stars defenseman Jani Hakanpää.
"I don't know the actual injury. I know it's upper body, to be honest," Boughner said. "I want to go in and check right now. We will [know] more tomorrow, but I think he's just getting a test and we'll figure that out."
NOTES:Defenseman Brent Burns played his 625th consecutive game to surpass Patrick Marleau for most in San Jose history. … Sharks forward Andrew Cogliano had one hit in 15:18 in his first game against his former team. He signed a one-year contract with San Jose on July 28 after three seasons with Dallas. … Karlsson scored his 29th game-winning goal since his NHL debut in 2009-10, trailing Oliver Ekman-Larsson of the Vancouver Canucks (31) and Burns (30) for most among defensemen in that span. … Hertl scored his 165th goal to tie Jonathan Cheechoo for sixth in Sharks history. ... Stars forward Roope Hintz sat out with a non-COVID illness. … Dallas has killed 20 consecutive penalties in the past nine games.