Tkachuk pushed the lead to 3-1 at 7:48 of the third with a wrist shot from the left face-off dot after Norris stole Ivan Barbashev's backhand pass in the Blues zone.
"We give up the third goal there, same thing," Berube said. "We can't make that play. Turn it over, it's in our net."
Alex Formenton scored into an empty net at 17:13 for the 4-1 final.
"I think it's much like the Vegas game," Senators coach D.J. Smith said, referring to the 2-1 loss to the Vegas Golden Knights on Sunday. "We had everyone going. We rolled four lines. The [defensemen] and the goaltending continues to be great. When you get that kind of goaltending, you have a chance every night. I thought it was one of our better second periods in a long time, and we put a lot of miles on them."
NOTES: Tkachuk led the Senators with five shots on goal and five takeaways in 15:15. ... Ottawa forward Zach Sanford had one shot on goal and played 15:15 in his first game in St. Louis since being traded to the Senators on Sept. 26. Sanford played four seasons with the Blues, winning the Stanley Cup in 2019. ... St. Louis forward Pavel Buchnevich (concussion protocol) left the game late in the third period, but Berube said he was fine when he was on the bench. … Perron has scored eight points (four goals, four assists) in his past seven games. ... St. Louis forward Jordan Kyrou had his seven-game point streak end. It tied his NHL career high. … Blues forward Mackenzie MacEachern had two shots on goal and played 8:16 in his season debut.