Tarnasky had his first career winning goal and combined with Vincent Lecavalier to score in a 48-second span late in a three-goal second period in a 4-1 win on Sunday.
"It's nice get a game winner," said Tarnasky, a role player who took seven shifts spanning less than four minutes.
His only shot caught Martin Brodeur off guard and turned out to be the biggest of the game for Tampa By, which has won 12 of 15.
With the score 1-1, Tarnasky skated down the right wing and had the puck poked off his stick behind the net.
"It took a funny bounce behind the net and I kept skating and there it was waiting for me," said Tarnasky, who stuffed the puck inside the post past Brodeur at 17:24. "It was a good goal and I think we got the momentum from that."
Brodeur didn't know what happened.
"I didn't see it, I was looking the other way," he said. "I thought we had control of the puck."
The goal was only the third in 64 career games for Tarnasky, who is just trying to help out nightly playing a supporting role to stars Lecavalier, Martin St. Louis and Brad Richards.
"Nick is a guy we have been trying to develop," Tortorella said. "He has come along pretty nicely.
"For him to chip in a goal against a team like that to give us the lead, it's important. We have been striving to get more goals from people other than our top guys. That's a huge goal, and then we come right back with another and take a two-goal lead, that's huge."
Lecavalier matched his career high with his 35th goal less than a minute later with Tampa Bay having an extra skater for a delayed penalty on New Jersey. Vaclav Prospal, who started the three-goal second period, found Lecavalier with a pass above the left circle and he ripped a shot just inside a post for a 3-1 lead.
Dan Boyle also scored for Tampa Bay and Johan Holmqvist had 21 saves in bouncing back from a bad game against the Rangers.
Scott Gomez scored for the Devils, who had a four-game winning streak snapped. The loss was only their third in regulation in the last 21 games (15-3-3).
"I don't think we were that bad," said Brodeur, who faced 27 shots. "It's just the bounces didn't go our way and they went into the net."
Boyle gave Tampa Bay more breathing room, scoring his 12th of the season at 56 seconds of the third period on a power play.
Lecavalier set up Prospal's tying goal 44 seconds into the second period, sending a pass from behind the net to his linemate all alone in front of Brodeur.
Gomez got a lucky goal 2:12 after the opening faceoff on a power play. His shot from a bad angle deflected off defenceman Cory Sarich and eluded Holmqvist, who was pulled in the second period of a 5-0 loss to New York on Friday night.
Against the Devils, only a bad bounce beat him. His biggest save came shortly after the Gomez goal, when he stopped Patrik Elias breaking in all alone.
"I think if you get down 2-0 against that team, it's awful tough," Tortorella said. "It's one of the key points of our pre-game meeting with them to try to open them up and get a lead."
Notes: Tampa Bay is 2-1 against New Jersey this season, and 13-4 against the Atlantic Division . . . The loss was only the Devils fifth at home in regulation this season (20-5-4) . . . The Lightning are 31-4-2 when they score three or more goals . . . Lecavalier also scored 35 goals last season . . . New Jersey centre John Madden missed the final 6:28 of the first period after being cut on the right side of his face by a shot.