"I don't know if you could've written it better," said Duchene, who missed the previous three games because of the birth of his first child, Beau David Newell Duchene. "It's a very special feeling. … I think I play my best when I'm light and happy. This week's been the best week of my life."
Ryan Dzingel had a goal and an assist, and Anders Nilsson made 30 saves for the Senators (18-24-5), who won for the third time in four games.
WATCH: [All Avalanche vs. Senators highlights]
"We had some huge efforts from everybody tonight," Duchene said. "[Nilsson] was outstanding, [Jean-Gabriel Pageau's] line did a really good job against their top line. I thought, top to bottom, we were outstanding."
Nathan MacKinnon had a goal and an assist, and Semyon Varlamov made 26 saves for the Avalanche (21-18-8), who lost for the 10th time in 12 games (2-8-2).
"We can't be coaching effort; it's almost February," Colorado coach Jared Bednar said. "The effort's not there at the start of the game for whatever reason. There's nothing else to it, you can't look past that. That's a prerequisite to everything else."
Brady Tkachuk gave the Senators a 1-0 lead 2:06 into the second period when he scored from the edge of the crease. Mark Stone made it 2-0 at 3:13 when he redirected a Cody Ceci point shot and the puck barely rolled over the goal line.