Saad made it 3-0 at 14:15 of the second period off a rush, beating Forsberg through the pads from the left circle.
Chabot thought he had cut the deficit to 3-1 for the Senators with 33.4 seconds left in the second, but the Blues challenged the play for offside and video review determined that Ottawa forward Nick Cousins preceded the puck into the zone.
"Yeah, it was [a pretty easy call to make]," Montgomery said. "As soon as the puck went in, already they were saying, 'I think this was offside, hold on.' Ten seconds later, they confirmed it."
Saad completed his third NHL hat trick at 18:07 for the 4-0 final, keeping the puck on a 2-on-1 with Alexandre Texier.
“I told ‘Tex’ that I wanted that one pretty badly,” Saad said, “so I’m happy it went in.”
The Senators won’t play again until Tuesday when they complete the marathon road trip against the Detroit Red Wings. The trip was necessitated by the IIHF World Junior Championship being played in Ottawa.
“I’m not going to use that as an excuse,” Senators coach Travis Green said. “They get four out of their [top players], and we’ve got to find a way to get some more offense out of our group. We're playing a little defensively, but we've got to create more. It’ll be good to get back home after a trip like this, where, yes, out of the past eight games, you come out .500, but now back home for a little bit before heading back to Detroit. Yeah, it’ll be good to get a couple practices under our belt and get back on the road for another game.
NOTES: Saad didn’t have a point in his previous 10 games and in the 19 games prior, he had just two assists. … Blues defenseman Ryan Suter played 20:44 and was a plus-2 in his 1,484th NHL game, which tied him for 25th all-time with Carolina Hurricanes coach Rod Brind'Amour. … Holloway has eight points (four goals, four assists) in his past five games.