OTTAWA -- Heading into a third-period power play, Guy Boucher wanted the Tampa Bay Lightning to be as concerned about preventing a goal as adding to their two-goal lead.
The rookie NHL coach could only look on as the Ottawa Senators made his worst fears come true.
Shannon's deke spoiled Dwayne Roloson's shutout bid, drawing Ottawa within 2-1.
"We had total control of the game and the only thing I said on that power play was, 'We can't get caught,' and that's exactly what happened," Boucher said.
Nick Foligno tied it with his 12th goal at 16:05.
Spezza lost control of the puck on a breakaway but the puck trickled through Roloson for the winner.
"I had lots of chances and I finally got one on a mistake," Spezza said.
Curtis McElhinney stopped 34 shots in his second straight start and fourth in five games for Ottawa. McElhinney, claimed on waivers from the Lightning on Feb. 28, made 33 saves in a 3-1 win over New Jersey on Thursday.
Vincent Lecavalier and Dana Tyrell scored for Tampa Bay, which is on a 2-4-4 skid.
"We were playing a pretty solid game, and then when you get scored on on the [power play], the momentum just shifts. That's probably the difference right there," said Lecavalier, who got a major and game misconduct for slashing P.K. Subban late in the first period of Thursday's shootout loss in Montreal.
Tampa Bay remained in fifth place in the Eastern Conference with 89 points, one behind Pittsburgh.
Roloson made 31 saves, including a sprawling stop on Chris Neil late in the second.
The 41-year-old goalie appeared destined for his fifth shutout in 27 games with Tampa Bay, since he was acquired in a Jan. 1 trade with the New York Islanders, until Shannon beat him on a deke with 7:33 left in regulation.
Roloson denied Bobby Butler with another huge stop moments later but Foligno tied it with 3:38 left.
"I think anytime you lose a game it's frustrating, but for us we have to look at the adversity we've gone through and find a way to win those games," Roloson said. "They are a team that works hard, they put pucks in the net and crash hard, so that's how they got their last two goals."
Ottawa (27-36-9) is last in the East and 28th overall in the NHL.
Steven Stamkos, who leads the league with 43 goals, drove a slap shot off the post on a Lightning power play in the first.
Roloson faced just three shots in the first, including a pair in the final 28 seconds.
Nate Thompson set up Lecavalier's goal with a pass that found the Tampa Bay captain behind the Ottawa defense. Lecavalier drove in alone and fired a wrist shot past McElhinney 6:32 in.
Stamkos came close to making it a two-goal lead with a drive off a faceoff seconds after Senators right wing Butler was sent off for hooking at 8:59.
Tyrell made it 2-0 with his sixth goal 7:42 into the second.
Roloson had no shutouts and was 6-13-1 in 20 games with the Islanders, despite a 2.64 goals-against average and a .916 save percentage. ... McElhinney dressed as Roloson's backup for two games from Feb. 25-27 but didn't play with the Lightning after he was acquired from Anaheim for G Dan Ellis. ... Senators D Sergei Gonchar left in the second period with an undisclosed upper body injury and didn't return.