Kyle Clifford scored for the Kings (17-25-3), who have lost four of five. Jonathan Quick made 23 saves.
Senators center Colin White sustained an apparent upper-body injury on a hit from Kings defenseman Jake Muzzin in the first period. White will return to Ottawa for further examination, coach Guy Boucher said, and is expected to miss at least two weeks.
The Senators were also playing without center Matt Duchene (personal) and defenseman Ben Harpur (upper body), but they received a complete team effort to overcome those absences, Tierney said.
"I thought we had good momentum from last game coming into this game," Tierney said. "Obviously Colin going down early, a lot of guys had to step up and play some big minutes, so I thought the whole team gave a 60-minutes effort. Every forward, every D, goalie, everybody was going."
Tierney gave the Senators a 2-1 lead at 16:40 of the second period, shooting through contact from Nate Thompson and beating Quick with Alec Martinez providing an inadvertent screen.
Mikkel Boedker had an assist, his 200th in 663 NHL games.
Christian Wolanin made it 3-1 at 1:22 of the third period. He has at least one point in each of his past four games.
Tierney scored into an empty net at 19:02 for the 4-1 final. He has five points (two goals, three assists) during a three-game point streak.
Clifford put the Kings ahead 1-0 at 3:47 of the second period, tipping Muzzin's shot past Nilsson.
Bobby Ryan tied it at 1-1 on a power-play goal at 14:59. He has seven points (three goals, four assists) during a six-game point streak.
"I think we kind of let up after we scored our first goal and let them into the game," Muzzin said. "They got two and then we just couldn't get back into it. It's disappointing, frustrating. We can't let teams off the hook. We let them back into the game, and they took advantage of it."
