Alexey Toropchenko gave St. Louis a 3-1 lead at 16:43, redirecting a wrist shot from Marco Scandella at the point that found its way through traffic.
Panthers forward Ryan Lomberg had a goal disallowed at 2:30 of the third period after video review confirmed his stick was above the crossbar.
Buchnevich scored an empty-net goal at 16:51 for the 4-1 final.
“Overall, it was a great response for our group,” Kyrou said. “We came out and had a strong start, and that is what we wanted to do after a slow start against Tampa.”
The line of Buchnevich, Thomas and Kyrou combined for eight points (three goals, five assists).
“It was fun to watch,” said Hofer, who made 12 saves in the third. “They were real good tonight and when they are going, we are really hard to play against. They were great.”
NOTES: It was the sixth time Thomas had three assists in an NHL game. … Blues defenseman Colton Parayko blocked six shots in 24:16 of ice time. … Panthers forwards Matthew Tkachuk and Aleksander Barkov, and defenseman Brandon Montour were each minus-3. Barkov won 14 of 17 face-offs (82.4 percent). … Florida forward Carter Verhaeghe had seven shots on goal.