Senators forward Clarke MacArthur played his first game since sustaining a concussion Oct. 14, 2015.
"I wasn't sure I was going to get back," the 31-year-old said. "It's great to get back with the guys. Obviously it's a big win, so it's nice. I wanted to play … the hurdles to get over everything ... very thankful for the organization to give me a chance to get back."
Karlsson gave the Senators a 1-0 lead at 12:59 of the first period with his 17th goal of the season.
Pyatt scored 7:49 into the second period to give the Senators a 2-0 lead. He took a puck tipped to him in the left wing circle by Jean-Gabriel Pageau. Pyatt's shot appeared to changed direction after hitting the stick of Red Wings defenseman Danny DeKeyser.
Karlsson, who missed the past two games with an upper-body injury, left the game halfway through the third period before returning to the bench. He did not play another shift.
"Nothing really," Karlsson said. "I'm watching guys like [Fredrik] Claesson and [Ben] Harpur especially, and they played really well yesterday and even better today. The guys did a great job in controlling the game and we felt it wasn't really necessary to use me at the end, unless we really needed to, and it never got to that point. Just took some ice time off and rested up."