"It was an important game for us," Sharks coach Peter DeBoer said. "I thought we really wanted to concentrate on having a good start. Obviously last game, getting down 3-0 early against Carolina wasn't the way we wanted to start here at home. I thought we fixed that tonight."
Couture gave San Jose a 1-0 lead at 12:55 of the first period with his 15th goal of the season. He took a pass from Kevin Labanc on a rush and beat Anderson with a wrist shot from the left circle.
San Jose extended its lead to 2-0 at 5:31 of the second period when Vlasic beat Anderson with a slap shot from the right point.
The Sharks made it 3-0 at 14:41 of the second period on Karlsson's fifth goal of the season, second in two games. Joe Pavelski passed from below the goal line to Karlsson in front, and he scored on a snap shot.
Dell is 5-3-1 this season after his third NHL shutout. Martin Jones expected to start against the Minnesota Wild on Sunday.
"He's been great every time he goes in the net," Vlasic said of Dell. "We have a lot of confidence in him, and he has confidence when he goes in. He doesn't play as much as [Jones] does, but when he's in it's like he's there every night."
Pavelski deflected Couture's shot to make it 4-0 at 3:24 of the third period, and Hertl scored a power-play goal at 17:38.
"Another bad game by us," Senators forward Mark Stone said. "We've got to find a way to get out of it. The bottom line is, you can't keep playing like this and expect to win. We're going to find a way. It's just a matter of how, and we've got to find that way."