Hammond, 27, said he felt better as the game progressed. He made his best save on a Pacioretty break down the left wing with six minutes left in the first period after a Karlsson turnover at the Montreal blue line.
Hammond was helped by Canadiens forward Brandon Prust hitting the post with a wide-open net five minutes into the game.
“I was able to get comfortable early. Every shot that came my way I felt I settled in even more," Hammond said. "Throughout the game I started just feeling in the zone, I guess.
“I think maybe the first save that kind of got me into the game was the Pacioretty breakaway in the first. That was really the first one that was kind of a reminder that you can do it, I guess. Obviously one of the best players in the League coming down on you and you stop him. That was the cool part of it.”
Senators coach Dave Cameron said he was happy for Hammond, who was called up when No. 1 goaltender Craig Anderson injured his hand Jan. 21. Hammond got the start after goaltender Robin Lehner was injured in a collision with teammate Clarke MacArthur on Monday.
Chris Driedger was called up from the Evansville IceMen of the East Coast Hockey League to back up Hammond.
Cameron said there was no update on the condition of Lehner or MacArthur on Wednesday. Pageau was recalled from the Binghamton Senators of the American Hockey League after one game in the minors and took MacArthur’s spot.
“Like I said today, [Hammond] should be pretty excited, and I think that’s how he played," Cameron said. "He battled, he was real solid for us. He stopped them every way possible, he used his head a couple of times when pucks went off it.
“When you see a goalie like that come up from the minors, and he’s been here for two-plus weeks, with all the shots he’s taken every day in practice … with everybody who stays out extra, he stands out there and helps out in whatever way he can … he’s a real easy guy to cheer for, and real excited for him.”
The Canadiens (37-15-4) continued to struggle against non-playoff teams. They are 11-4-1 in their past 16 games and the five losses have been to teams not in a Stanley Cup Playoff position (twice to the Senators, and to the Arizona Coyotes, Buffalo Sabres, and in overtime to the Edmonton Oilers).
Canadiens defenseman Alexei Emelin was injured 20 seconds into the game and did not return. Emelin collided with Stone and fell, striking his right shoulder at the base of the boards in front of the Montreal bench.
Pacioretty gave Hammond credit but said the Canadiens didn’t do enough enough work around the Senators net.
“I think we made it a little bit too easy on their goalie. We have to get some screens and some second and third chances," Pacioretty said. "It’s the same story too often. We have to find ways to put the puck in the net especially when we have [Tokarski] back there. We’ve left him out to dry too many times this year.
“It’s frustrating because he’s a great goaltender and he does all the right things. We give up too many chances and we haven’t been able to score with him in there. That’s on the players in this room and nobody else.”
It was a wide-open game with good chances at both ends of the rink.
“[Hammond] deserved a lot of credit. We threw a lot of pucks to the net and he made some key saves, but that’s [not] the type of hockey we want to play, especially at this time of the year," Therrien said. "I thought we gave up too many scoring chances and quality ones.
“It could be a times we didn’t manage the puck well, our coverage was not good enough and we left Tokarski by himself a few times. If you expect to win games in the National Hockey League, you can’t do that.”
Montreal defenseman P.K. Subban left the game late in the second period after he was injured blocking a shot, but he returned for the third and played a total of 30:45. On Saturday against the Toronto Maple Leafs, he played a career-high 35:21, the most in an NHL game this season.
The Senators took a 2-1 lead at 18:13 of the second period on just the kind of play Therrien was talking about. Pageau finished off a nice passing play that saw Erik Condra feed Karlsson at the left point.
Karlsson found Pageau breaking for the net in front of Montreal defenseman Andrei Markov and Pageau was free to tip the pass behind Tokarski for his third goal of the season.
Stone barged into the crease to get to a loose puck on the power play at 9:27 of the third period to make it 3-1.
Beaulieu scored the first goal his NHL career at 14:25 of the third period when his shot deflected off a Senators player and bounced past Hammond to make it 3-2.
The Senators opened the scoring at 11:26 of the second period on Michalek’s goal, but Pacioretty tied it 8 seconds later, a Senators record for the fastest goal by an opponent after an Ottawa goal.
The first period was scoreless, but there were three posts or crossbars hit and each goaltender made good saves.
The Senators will try to win two games in a row for the first time since Dec. 29-Jan. 3 against the Panthers at Canadian Tire Centre on Saturday.