With the score tied 1-1 early in the third period, Eller thought he gave the Canadiens the lead when his shot from a tight angle seemingly trickled under a sprawling Pekka Rinne's arm.
Instead, the goal was disallowed, and the Nashville Predators went on to beat the Canadiens 2-1 on Saturday night at the Bell Centre.
"The puck was inside," said Eller. "(Rinne) had his glove on it, so technically you couldn't see it was inside. But if it's not outside the line, it's got to be inside. It's logic."
The decision on the ice confirmed Eller's suspicion, that the puck had crossed the line. But the referees, with the help of video replay, overturned the initial call.
"In my mind, I know the puck was inside," said Eller.
The Canadiens went on to dominate the third period, but wouldn't find the back of the net again.
Nashville's Seth Jones would, though, as he scored the eventual winner.
Rookie defenceman Jones, who's already turning heads this early in his career, was selected fourth overall in the 2013 entry draft by the Predators. He now has four points on the season.
"We've been very fortunate," said Predator head coach Barry Trotz. "We really got a special player in Seth Jones. We saw what he can do. He played big minutes tonight, scored the winning goal. He's earning his own stripes."
Jones' goal tarnished a solid performance by Carey Price, who made 35 saves in the loss. Price has never beaten Nashville in his career.
"Price was big for us," said right-winger Brendan Gallagher, the Canadiens' lone goal scorer. "We had a chance to win it late. But the only reason that was, was because he was so good early."
Nashville captain Shea Weber opened the scoring with the man advantage at 12:31 of the first period. His cross-crease pass bounced off Montreal defenseman Josh Gorges and deflected past a helpless Price.
Gallagher made it 1-1 at 7:02 of the second, finishing up a scramble in front of the net by lobbing the puck over Rinne.
After Eller's disallowed goal, Jones walked into the Montreal zone, dangled the puck Gorges with a nifty move, and fired home his second goal of the season at 18:33 of the final period.
"On the winning goal, it was bad coverage — pretty simple," said Montreal head coach Michel Therrien.
Rinne made 28 saves for the win.
The loss put an end to the Canadiens' four-game win streak.
Montreal also lost forward Daniel Briere, who suffered a concussion after a second period hit by Nashville's Eric Nystrom. Briere has a history of concussions, sustaining one in March, and another in January of last year.
"I think it was an accident," Therrien said. "The two players ran into each other. I don't think the Nashville player was targeting his head."
Brandon Prust also left the game with an upper-body injury.
Before the game, Habs assigned defenseman Nathan Beaulieu to Hamilton.
The Canadiens welcome the Edmonton Oilers to the Bell Centre on Tuesday.