With Anaheim leading the Senators 3-2 late in the second period, Alfredsson steered a partially blocked shot from Wade Redden past Ducks goaltender J.S. Giguere with his skate at the 16:14 mark.
The goal was initially waved off by referees Paul Devorski and Dan O'Halloran, but after a review, it was allowed to stand.
"I felt it was a goal all along," Alfredsson said of his playoff-leading 11th goal. "I think from the ref's position, he thought it went off my skate a but to me it felt (like) I never kicked the puck, never lifted my foot."
It proved to be a crucial point in the game and, from the Senators' point of view, possibly the series.
They struck again just more than two minutes later to take their first lead of the night and went on to win 5-3 to cut the Ducks' lead in the best-of-seven Stanley Cup final to 2-1.
Given the reaction of the Senators' bench and the crowd of 20,500 at Scotiabank Place, which erupted when the goal was allowed to stand, it also provided a great deal of relief.
"Goals like that, they're at the discretion of the officials upstairs," Senators right-winger Mike Comrie said. "When Alfie came to the bench, he said he didn't make a kicking motion. He directed the puck in, which is legal, but you never know when you're sitting on that bench. It was a great bounce for us and we kept playing hard after we got that goal.
"It's the time of the year where every little play counts and those type of goals aren't pretty, but they all count on the scoresheet."
Not surprisingly, the Ducks disagreed with the ruling.
"Well, obviously the league felt it wasn't kicked in, simple as that," Ducks coach Randy Carlyle said. "Sometimes those things go for you. Tonight it went against us. Obviously we felt that there was a kicking motion for our point of view. a But that's the way it is. They make the call and you have to live with it."
The goal also provided some relief to the Senators' No. 1 line of Alfredsson, Dany Heatley and Jason Spezza, which was taking plenty of heat for not producing enough in the first two games of the series.
"It's huge," Spezza said. "We're down a goal at that point, our line had a lot of chances up to that point and then to get the goal on a nice bounce like that was good and we carried the momentum the rest of the game."