Arsenal manager Arsene Wenger hit out at Romanian referee Ovidiu Alin Hategan for sending off striker Olivier Giroud after the Gunners slumped to a 2-1 defeat in their Champions League Group F opener at Dimano Zagreb.
The France forward missed a couple of early chances before collecting two cautions in the first half, for dissent and then tripping Daniel Ivo Pinto.
Dinamo went on to record their first Champions League win since September 1999, having taken the lead against the run of play with an own goal from Alex Oxlade-Chamberlain when the ball bounced back off him past goalkeeper David Ospina, who had saved Josip Pivaric's shot.
The hosts doubled their lead through a powerful header by Junior Fernandes.
Despite a late goal from substitute Theo Walcott, Arsenal were left to reflect on another frustrating European away performance.
Wenger - who had made half a dozen changes with one eye on Saturday's Barclays Premier League trip to Chelsea - pulled few punches in his assessment of the official.
"We were a bit unlucky tonight," the Frenchman said. "I believe the first goal is offside and after the sending-off is very harsh.
"We were not at our best, but nor was the referee tonight.
"The first yellow is Giroud's fault because he protested, even if it was not a foul against him. But after he should not have responded to the referee.
"The second yellow card, he is unlucky to touch the guy - he did not see him. It was accidental completely, but it happened.
"I don't understand the referee. It has to be on purpose, a foul on purpose. Then the referee should have given many yellows tonight."
Wenger, however, accepted Arsenal were well below the required performance.
Dinamo Zagreb 2 Arsenal 1 player ratings
Dinamo Zagreb 2 Arsenal 1 player ratings
1/11 Arsenal: David Ospina 5/10
Hardly culpable for either Zagreb goal, though you might have expected Petr Cech to hold on the initial effort for the first. Or at least not palm it back into the danger area.
2/11 Debuchy 6
Started the game desperate to prove he could do all Hector Bellerin can and more. Whilst he looked bright going forward he was dragged well out of position for Zagreb’s opener.
3/11 Gabriel 7
On more than one occasion he was called on to pull off spectacular clearances or interceptions just to keep Zagreb from adding to their advantage. He won plenty of aerial challenges and made one excellent sliding challenge.
4/11 Koscielny 5
Was late to the cross for Zagreb’s second to blot what had previously been a perfectly acceptable performance from the defender. But Arsenal’s defensive leader should not be making careless mistakes at such crucial moments.
5/11 Gibbs 5
Another who could have done much better for the second goal, he showed everything that has allowed Monreal to win the left-back spot, attacking intent coupled with defensive disorganisation.
6/11 Cazorla 4
Dispossessed on no fewer than four occasions this was nowhere near good enough from Arsenal’s creative conductor, who was also caught out of position time and again.
7/11 Arteta 3
The Arsenal captain’s legs are gone, and it showed time and again at the Maksimir. When Zagreb countered the visitors’ defence found themselves with no cover and no chance.
8/11 Oxlade-Chamberlain 7
The only outfield player to end the game in credit, he never stopped running and stretching the play. If he had the lofty reputation of his colleagues he would never have been substituted.
9/11 Ozil 4
Showed everything that infuriates Arsenal fans when he is at his worst. Shrugged off the ball on more than one occasion and seemed to wander aimlessly as he slowed down play.
10/11 Sanchez 4
An assist is all well and good but even that showed his struggles in one of his worst games for Arsenal. His touch was heavy and too often he gave the ball away under little pressure.
11/11 Giroud 1
After missing a sitter he picked up two truly idiotic bookings to leave his colleagues in no-man’s land. Totally and utterly unacceptable from the striker as Arsenal looked to get back into the game.
"We have for a part to look at ourselves also, because the second goal kills our game. On the corner we were guilty not to defend it well," he said.
"When you don't win the game you have to look at yourself and think you haven't got it right.
"I don't believe the players who came in had a bad game but it didn't work, it didn't work.
"I have to analyse that well. It is very difficult to give a definite answer straight after the game."
Arsenal next host Olympiacos before a double-header with group favourites Bayern Munich.
Wenger said: "Mathematically, we can qualify without any problem if we produce our performances that we want at home.
"Overall, I believe we have problems to start in every competition this season. We had problems in the Premier League and again in the Champions League tonight, but I am confident we can put that right in the next five games."
Dinamo Zagreb manager Zoran Mamic had warned his side had no intentions of giving Arsenal an easy ride at the Maksimir Stadium.
Mamic praised the way Dinamo - who have never qualified for the knockout stages - went about their business.
He said: "I am very happy and proud. I thank the team for doing what I told them and the fans for pushing us when Arsenal had us under pressure.
"Now they have such confidence because see how good they really are.
"After this we are ready for anything which might come, but are also aware of the strength of the group and cannot fall into euphoria."
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