After an overtime loss Saturday in Montreal and a 3-1 defeat on home ice to the Colorado Avalanche, the Senators walked away from their weekend games with just one point.
"It was a big weekend for us and we lose both games," said Senators captain Jason Spezza. "We played good but it's a different way to lose every night and results are the only thing that matter right now.
"We didn't turn the puck over much, we created a lot but again. It just wasn't enough to win the game and it's unacceptable."
Andre Benoit, Nick Holden and John Mitchell scored for the Avalanche (44-19-5) while Matt Duchene had two assists as Colorado picked its third win in four games, and seventh in its past nine.
Semyon Varlamov made 38 saves. The Colorado goalie was just six seconds away from his second shutout of the season and 13th in his career until Mika Zibanejad scored at 19:54.
Robin Lehner made 19 saves in his second straight start for the Senators (28-26-13) since Craig Anderson was injured last week in a loss to the Nashville Predators.
"Response to the game (Saturday) was positive," said Senators coach Paul MacLean. "A lot of the statistical things were positive, but at the end of the day it's the score that matters and we gave up three goals and only scored one.
"We created opportunities to score but I don't think we got to their net as hard as we could have and we missed the net a number of times."
Nursing a 1-0 lead heading into the third period, the Avalanche were awarded their first and only power play of the game when Ottawa forward Chris Neil closed his hand on the puck and was called for delay of game.
Duchene took a shot during the man advantage that Lehner stopped but the rebound went right to Holden, who was alone at the side of the net and scored at 3:10.
"The power play was sharp again, we had only one opportunity but scored a very important goal for us," Avalanche coach Patrick Roy said before praising the play of his goaltender.
"He was very solid and he made some very key saves. I thought we had too many turnovers in that second period. Our goalie was without a doubt the first star of the game."
The Senators pressed throughout the period, but the game was virtually over when Mitchell beat Lehner from in tight with less than three minutes to go in the game.
Following a scoreless opening period, Ottawa held a heavy edge in play over the second 20 minutes.
Ottawa outshot the Avalanche 20-8 in the second period but it was former Senator Andre Benoit that scored the period's only goal and gave Colorado a 1-0 lead in the process.
The Avalanche broke out three-on-one late in the period and after receiving a drop pass from Patrick Bordeleau, Benoit moved into the slot and put a shot over the shoulder of Lehner.
"It's always fun to score against an old team and I had lots of family and friends here. Hopefully they keep going in," said Benoit, who is from St. Albert, about 30 minutes from Ottawa.
"It was a big game and we were able to get a win. We have to keep this going now."
Benoit was a fan favourite in Ottawa despite playing just 41 games for the Senators over two seasons. He has played in 66 of Colorado's 68 games this season and has nine goals in 107 career games. Four of those have come in his last nine games.
Notes: Matt Kassian, Patrick Wiercioch and Craig Anderson were scratches Sunday for the Senators. Scratches for the Avalanche were P.A. Parenteau, Paul Stastny, Paul Carey, Ryan Wilson and Reto Berra…Senators defenceman Erik Karlsson played his 300th NHL game on Sunday. Forward Kyle Turris played in his 300th game Saturday in the Senator's loss to Montreal…The last time the Avalanche recorded 44 wins in a season was back in 2007-08…The Avalanche are the only team in the NHL to sore at least one goal in every game this season.