Joel Armia's power-play goal at 19:27 increased the lead to 4-1.
Brett Kulak made it 5-1 at 8:14 of the third period. He took a touch pass from Nick Suzuki after entering the zone on the right side before cutting into the slot to score with a wrist shot.
"We battled, we worked hard, but a tough outcome," Senators forward Adam Gaudette said.
NOTES: Anderson had an assist on Kulak's goal after missing two games because of a lower-body injury. "Obviously there is some stiffness, but overall I felt pretty good as the game went on and had my legs out there," Anderson said after playing 16:06. ... Caufield, who has scored seven points (five goals, two assists) during his streak, is the fifth Montreal rookie in the past 20 years to have a goal streak of at least four games (Jesperi Kotkaniemi (2018-19), Matt D'Agostini (2008-09), Chris Higgins (2005-06), Marcel Hossa (2002-03)). No Canadiens rookie has had a longer goal streak since 1951-52, when Bernie Geoffrion scored in five straight games on his way to winning the Calder Trophy voted NHL rookie of the year. ... Suzuki has scored 18 points (eight goals, 10 assists) in his past 13 games. ... Canadiens forward Jonathan Drouin did not have a point in 13:57 after missing 22 games because of a wrist injury he sustained on Jan. 20.