Jaroslav Halak made 28 saves for the Canadiens, who gave coach Jacques Martin his 550th career win in the team's first home game since the Olympic break.
Glen Metropolit notched his career-high 15th goal and added an assist. Benoit Pouliot also scored as Montreal won its third in a row - including the last two games of a 3-1 road trip - to strengthen its hold on seventh place in the Eastern Conference with 72 points.
"That's what it takes to win - everyone's chipping in," Gomez said. "We're getting healthy bodies and we're starting to look like the team we should have been all year."
Steven Stamkos scored his 41st goal for Tampa Bay. He set a Lightning record with his 17th power-play goal and extended his club-record point streak to 17 games.
"None of that's going to matter if we're not in the playoffs," Stamkos said. "I'm just trying to do my part and help this team win and that's creating offense. I'm going to keep doing that for the rest of the year."
Matt Walker scored his first goal of the season and Martin St. Louis also tallied for the Lightning, who beat Atlanta 6-2 on Saturday to end a season-high, five-game losing streak.
Tampa Bay is in 11th place overall in the East with 65 points, five behind eighth-place Boston.
Antero Niittymaki, who stopped nine of 13 shots, left after Darche's goal at 7:33 of the second put Montreal ahead 4-1. Mike Smith made 14 saves on 15 shots in relief.
Despite crashing headfirst into the boards on Saturday, St. Louis was in the lineup and scored late in the third to draw Tampa Bay within two.
Ryan Malone and Zenon Konopka, however, missed the game because of injuries. Malone was sidelined by an upper-body injury. Konopka sat out his second straight due to back spasms.
Canadiens center Maxim Lapierre served the third game of his four-game suspension for his hit from behind on San Jose's Scott Nichol.
Metropolit opened the scoring on a power play 2:50 in. Gomez carried the puck down the left side of the Lightning zone and behind the net before feeding a pass to Metropolit, who put a quick shot past Niittymaki from the right side.
"Scott had so much speed going down the wall and I kind of timed it where I slowed down a bit so I could one-time it," Metropolit said. "He made a great pass."
Gomez made it 2-0 at 12:02 with his 12th goal. He emerged from the left corner and beat Niittymaki with a shot between the pads.
Stamkos drew the Lightning within 2-1 with an unassisted effort 3:47 into the second. Montreal defenseman Hal Gill's clearing attempt went right to Stamkos, who fired a wrist shot over Halak's right pad.
"I mean, it's a good pass, right on the tape. Obviously he was trying to clear it," Stamkos said. "I just got lucky and it went on my tape and I had an open net. Probably one of the easier ones of the year."
Gomez earned his third point of the game 41 seconds later with an assist on Pouliot's 16th goal at 4:28. That gave the Canadiens a 3-1 lead.
Darche, who played 73 games for Tampa Bay during the 2007-08 season, made it 4-1 when he redirected Metropolit's centering pass beyond Niittymaki.
Walker scored for the first time in 52 games this season midway through the second. Mark Parrish assisted on the goal for his first point in five games since he was called up from Norfolk of the AHL.
Darche added his second of the game when he beat Smith 3:26 into the third to put Montreal up 5-2.
"You want to show them that they might have made a mistake by not bringing you back, but they have great players over there," Darche said. "At this point of the year I'm just happy to contribute to a win. If it's against your former team, it's just a little cherry on top of the sundae."
St. Louis netted his 24th with a backhander past Halak at 18:53.
NOTES: Brian Bradley and Vincent Lecavalier shared the Lightning's previous single-season record of 16 power-play goals. ... Metropolit set his previous career high of 14 goals in the 2006-07 season when he scored 12 with Atlanta and two with St. Louis. ... Martin, who has also coached St. Louis, Ottawa and Florida, has 435 losses, 119 ties and 62 overtime losses in 1,166 regular-season games.
|PPG - Glen Metropolit (15) ASST: Scott Gomez (37), Jaroslav Spacek (17)|
1 - 0 MTL
|Scott Gomez (12) ASST: NONE|
2 - 0 MTL
|PPG - Steven Stamkos (41) ASST: NONE|
2 - 1 MTL
|Benoit Pouliot (16) ASST: Scott Gomez (38)|
3 - 1 MTL
|Mathieu Darche (4) ASST: Glen Metropolit (13), Andrei Markov (18)|
4 - 1 MTL
|Matt Walker (1) ASST: Mark Parrish (1), Stephane Veilleux (5)|
4 - 2 MTL
|Mathieu Darche (5) ASST: Tomas Plekanec (44), Andrei Markov (19)|
5 - 2 MTL
|Martin St. Louis (24) ASST: Steven Stamkos (37), Kurtis Foster (25)|
5 - 3 MTL
|Power Play %||33.3%||0.0%|
|% on Road||0.0%||0.0%|
|% at Home||33.3%||0.0%|
|Todd Fedoruk Too many men/ice - bench|
|Ryan O'Byrne Charging against Mattias Ohlund|
|Ben Maxwell Interference against Stephane Veilleux|
|Roman Hamrlik Cross checking against Steve Downie|
|Steve Downie Slashing against Travis Moen|
|Tomas Plekanec Slashing against Steven Stamkos|