Hoffman and Duchene raced for a 2-on-1 off the OT faceoff, and Hoffman slipped a backhand pass across the slot to Duchene, who pushed the puck past goalie Aaron Dell.
Brassard made it 5-3 in the opening minute of the third, beating Dell from a sharp angle. Duchene then scored off his backhand, and Hoffman tied it with his first goal in 15 games, midway through the period. The Senators had 17 shots on goal in the third period alone.
The Sharks took a 4-1 lead early in the second, scoring back-to-back power-play goals. Anderson gave up a big rebound and Tierney was there to pick it up, beating the goalie glove side on the first goal. Less than two minutes later, Burns took a great pass from Logan Couture and beat Anderson with a one-timer for his seventh of the season.
The Senators got one back on the power play as Dzingel found Stone, who beat Dell far side.
San Jose regained its three-goal lead on Hertl's second of the night when Anderson struggled to handle a bouncing puck on a wraparound and watched it bounce in through his legs.
San Jose scored the game's first goal while short-handed. Hertl, on a breakaway, scored his first of the game at the six-minute mark.
The Senators tied it on a nice goal by Dzingel, but the Sharks regained the lead just over two minutes later when Karlsson tipped in Joakim Ryan's point shot.
NOTES: Ottawa's Nate Thompson left early in the first with a lower-body injury and did not return. ... Ottawa C Zack Smith returned to the lineup after missing the last five games with a shoulder injury. D Fredrik Claesson was a healthy scratch. ... Sharks RW Joel Ward was a healthy scratch to give the veteran the night off.
Sharks: Play at Winnipeg on Sunday.
Senators: Host Tampa Bay on Saturday night.