Anaheim leads the best-of-seven series 2-1 with Game 4 set for Monday night at Scotiabank Place.
Alfredsson's goal stood up after a long video review after he reached back with a skate to redirect Wade Redden's point shot past Jean-Sebastien Giguere to tie the game 3-3 at 16:14. The goal was initially waved off, but replay officials saw otherwise.
"I felt it was a goal all along," said Alfredsson, who hadn't recorded a point since Game 5 of the Eastern Conference final against Buffalo. "To me, it felt like I never kicked the puck. I never lifted my foot.
"I was confident it was going to be a goal. At the same time you never know, but it felt like a goal."
Ducks head coach Randy Carlyle wasn't so sure.
"Obviously the league felt it wasn't kicked in," said Carlyle. "Simple as that. Sometimes those things go for you. That one went against us.
"We felt there was a kicking motion from our point of view. But I haven't really reviewed the replay from a bunch of different angles. They make the call and you have to live with it."
McAmmond then saw his centring pass accidentally knocked into the net by an errant Pronger clearing as the sell-out crowd of 20,500 went wild.
The goals highlighted a gripping match in which the two teams traded momentum in each period, with Anaheim dominating early in each of the first two period and Ottawa clawing back late.
After being held to two goals in the first two games in the series, the Senators showed more life than the Ducks, especially on the forecheck.
"The first two game we didn't have our legs," Senators forward Chris Kelly told CBC. "For us to be successful we need to get in the forecheck and in the their zone, and I thought we did better job tonight."
Anton Volchenkov's goal 8:22 into the final period after some dogged work by Ottawa's checking line made it 5-3 and sealed the victory.
A nasty third period saw McAmmond dazed by a Chris Pronger forearm shiver and a melee broke out after Ryan Getzlaf cross-checked Ottawa's Chris Neil.
Senators coach Bryan Murray said he wasn't told why Pronger wasn't penalized on the hit that knocked McAmmond out of the game with a head injury.
"They told me to go stand behind the bench," said Murray. "That was the explanation, pretty much.
"I guess I've been around too long, nobody listens to me anymore. I didn't get any explanation."
Mike Fisher also scored and Neil celebrated the birth of his daughter on Friday with his first goal since the opening game of the first round against Pittsburgh.
"He came in this morning, we knew he didn't get a lot of sleep," Kelly told CBC. "He was on cloud nine, his first girl. For him to score that first goal was definitely big."
Andy McDonald scored in the first, while linemates Getzlaf and Corey Perry had goals in the second for Anaheim. The Perry-Getzlaf-Dustin Penner line now has 35 points in 19 playoff games.
The first Stanley Cup final game in Ottawa in 80 years saw the Senators skate out to their loudest crowd of the playoffs thus far.
There was plenty of energy, but also a case of nerves as Ray Emery needed to make a big glove save off Penner from the low slot only two minutes into the game.
McDonald scored on a power play goal at 5:39 when he was set up alone in front by Teemu Selanne to beat Emery, who had lost his stick, with a wrist shot inside the right post.
It was the first power-play goal allowed by Ottawa in nine attempts in the series.
Ottawa stepped up the pressure late in the period and Neil was on the doorstep to bang Chris Kelly's pass just over the line to tie it at 16:10.
Perry came out from behind the net to slide one between Emery's pads 5:20 into the second period, but Fisher got it back 27 seconds later when he deflected Volchenkov's point shot.
Getzlaf pounded a big rebound from the slot past Emery at 12:22 for a 3-2 lead.
McAmmond did not return after the Pronger hit 2:03 into the third period. The team said he had a head injury. Pronger was suspended for Game 4 of the Western Conference final for ramming Detroit's Tomas Holmstrom's head into the glass.
Notes: With Chris Kunitz's return after missing seven games with a broken finger, Drew Miller sat out for Anaheim. Kunitz only lasted until the second period before leaving with a lower body injury. ... Ottawa made no changes from its Game 2 lineup. ... Surviving members of the Montreal Canadiens team that won five straight Cups from 1956 to 1960 received a nice ovation when introduced on the scoreboard in the first period. They were honoured by the NHL at a dinner Friday night. Art Ross trophy winner Sidney Crosby, Rocket Richard winner Vincent Lacavalier and Jennings winners Manny Fernandez and Niklas Backstrom sat with them. ... Russell Williams, a 99-year-old fan who watched the Senators win the Cup in 1927, was given a standing ovation when introduced in the second period.