Kerry manager Jack O'Connor was irked by a "bizarre" decision to award a Donegal point late in the first half after a shot which he contended had drifted "a yard or more wide".
On the half-hour mark, with the visitors leading by five points, Caolan McColgan struck a shot goalwards which the umpire on the near post signalled as a point. There was confusion on the sideline as the crowd appeared to believe the ball was wide of the left upright.
O'Connor, with a decent vantage point on the sideline, said he was adamant that the ball was clearly wide and reported afterwards that the linesman standing beside him agreed with this verdict.
Nonetheless, referee Liam Devenney eventually awarded the point after briefly going in to consult with his umpires.
The call wound up having ramifications as Donegal reeled in Kerry in the final quarter, Paddy McBrearty curling over a superb winning point deep into additional time.
The four-time All-Ireland winning manager said he didn't want to engage in sour grapes but insisted the officiating wasn't up to standard.
"Arra, it's not even (that I'm) angry. It was just a bizarre decision," O'Connor told RTÉ Sport after the game.
"The ball was a yard or more wide. I was standing beside the linesman and he said it was wide.
"And yet the umpire, after consulting with the referee, allowed the point. That cost us at the end of the day.
"That's what happens when you go to away grounds, you don't tend to get many breaks.
"I don't want to be seen to have sour grapes here but the bottom line is that shouldn't be happening in a Division 1 game. It was a bizarre decision."
"I don't want to be seen to have sour grapes here but the bottom line is that shouldn't be happening in a Division 1 game.
Outside of pre-season, the match is Kerry's first competitive defeat since their home loss to Tyrone late in last year's league.
"I've gone on record that we started training well behind most teams. Maybe the legs got us in the last quarter of an hour. But I thought the subs we put on lifted us again.
"There was a period in the game where we could easily have put Donegal away. But we didn't, we kept them in it. Once they got the smell of it, they drove on and McBrearty kicked a great score to win it.
"You just take every game as it comes. You don't want to lose any game. We'll be disappointed going down the road having lost this game today.
"The championship is a long way off. You have to take it game by game, step by step. That's what we'll be doing."
Kerry started only five of the team that began last July's All-Ireland final, with a completely changed forward line.
The most notable absentees were the Clifford brothers and Seanie O'Shea in attack, with O'Connor indicating afterwards that the front-rank forwards were unlikely to be back for another month.
"We played what was available," O'Connor said curtly.
"I don't think we'll have any extra player in the next week or two. It'll be more than a month before you see any new players.
"We want players for the present, whatever about the future! Look, happy enough with lads at the moment but disappointed to fall short."
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