"The game's fast and he's our fastest player," Senators coach D.J. Smith of Duclair. "He's making plays, certainly he's confident right now, and he's been reliable. Sometimes that's with confidence, sometimes with age, but he's been good for us all year."
Chris Tierney had a goal and two assists, and Anders Nilsson made 38 saves for the Senators (13-17-1), who had lost six of their previous seven games.
WATCH: [All Bruins vs. Senators highlights]
It was Ottawa's first win against Boston since a 2-1 shootout victory on April 6, 2017 (0-9-1 in previous 10 games).
"For sure they are (the best team in the League)," Smith said. "They're ready to win now and they came within a game of winning the Stanley Cup (last season). They have some high-end players and some guys that know how to win over there."
Patrice Bergeron scored in his return, and Brad Marchand and David Pastrnak each had two assists for the Bruins (20-5-6), who are 0-2-1 in their past three games after an eight-game winning streak. Tuukka Rask made 23 saves.
"We're going through a tough stretch in terms of getting our energy level where it needs to be," Boston coach Bruce Cassidy said. "If you're not competing hard on the puck, around the puck, on the puck, in this League, you're not going to beat anybody. Ottawa was just better than us. They won more races, they were more competitive early on. Now we eventually got to our game, but again, it's too late. We knew this would catch up to us, so another kind of learning experience for us."
Artem Anisimov gave the Senators a 1-0 lead at 1:35 of the first period, receiving a stretch pass from Dylan DeMelo and skating in on a breakaway before scoring with a backhand.