Iago Aspas had given Celta Vigo the lead with a trademark finish before Alonso was sent off shortly after the restart for a rash challenge on Ăker Muñoz, a decision that swung the contest. Kike Barja levelled from a corner soon after, and Osasuna completed the turnaround when Ante Budimir converted a penalty following a foul by Javi GalĂĄn.
Claudio GirĂĄldez was measured but clearly frustrated by the officiating call.
"The VAR understood it had to advise the referee, and after many replays and a lot of viewing, he decided it was a red card. You have to accept it, respect it. It's a fundamental decision in the game and it changes it, beyond GalĂĄn's penalty situation, which was also decisive and effectively killed us off.
"I understand it isn't very clear if it takes that long to decide, and in that case I would have chosen not to send him off, but I understand he can do it. That's how it went, it's football and we have to accept it," he said.
The Celta coach was more critical of his side's defending for the equaliser than the red card itself.
"We defended the 1-1 situation very badly, and that's what annoys me most about the match â we're in a numerical majority in the box, RaĂșl touches it in front and we lose our mark at the far post. Everything fell the wrong way and we have to accept it. Very happy with the last 20-25 minutes, in which I think we were better with a man less," GirĂĄldez said, reflecting on a first half he felt his side had dominated.
"I think we had absolute control for the first 45 minutes. We spent much more time above our opponent in terms of control, in terms of dominance. A sending-off changed everything and we didn't settle well afterwards, and that's what has upset me most about the match. We have more quality for the small number of chances we're creating. Points have slipped away and it's hard to understand how."
Osasuna coach Luis Miguel Ramis called the win a significant confidence boost on the road.
"Numerically, the three points are very important, and even more so now because they'll give us peace of mind. What gives you more confidence and calm are results, that's why this win is very important," he said, before explaining the message he had delivered to his players beforehand.
"Before the game I spoke to the players about how important it was to have the feeling that we can also compete with strength away from home, that we can look any opponent in the eye. This team is capable of doing that, and the stress from last season had left the lads a bit more withdrawn."
Ramis acknowledged that Alonso's dismissal shaped the outcome, saying it helped his side become "bolder, to dominate and feel a bit stronger," and felt the victory was deserved because Osasuna had "played with a lot of personality and a lot of maturity."