After the final whistle Arsenal players trudged around the pitch for the traditional lap of appreciation to mark their final home game of the season. The smattering of fans who had stayed to bear witness to this joyless formality did at least bid hearty farewells to Petr Cech, Aaron Ramsey and Danny Welbeck, none of whom will play a home game here again. Moments before that Arsenal had said goodbye to any realistic chance of finishing in the Premier League’s top four this season.

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Arsenal could yet make it if things get freakish on the last day of term – they would have to win big away to Burnley, for a start, and hope Tottenham lose heavily at home to Everton – but Unai Emery accepts that the only realistic route to next season’s Champions League is to win the Europa League. “Our first target was [to finish in the top four] in the Premier League so we are very, very disappointed,” said the Arsenal manager. “But we need to keep a strong focus for Thursday in Valencia, we can still do something important.” His side take a 3-1 lead into that second leg but will need to show more fortitude than they did here if they are to preserve it.

This was the latest instalment of a race for the top four that seems more like a lobbying campaign to have the number of English clubs in the Champions League reduced. Arsenal came into the game after three domestic defeats and, despite taking an early lead through a penalty by Pierre-Emerick Aubemeyang, came close to suffering a fourth, as Pascal Gross miskicked from three yards in the dying minutes with the goal at his mercy.

Brighton had drawn level half an hour earlier when Glenn Murray converted a penalty given away in daft fashion by Granit Xhaka. That was Brighton’s first away goal in five matches, and earned them their first point at the home of a top-six team this season.

The disintegration of Arsenal’s form at the Emirates, which had been impressive until they lost to Crystal Palace in their previous game, attested to a team whose limitations had at last come home to roost.

Brighton, meanwhile, came into this game liberated of the threat of relegation thanks to Cardiff City’s defeat on Saturday. Perhaps Chris Hughton would free up his players to attack with gusto? That looked a zany notion after the opening minutes, during which Brighton’s green-clad players massed around their own box like soldiers guarding a precious asset.

Guarding it badly, too. Arsenal nearly took the lead within two minutes after Alexandre Lacazette demonstrated one of the skills that led to him being announced as the home club’s player of the season before kick-off, dodging between the giant trees in the visitors’ area before laying the ball back to Henrikh Mkhitaryan, whose low shot struck a post.

Brighton’s resistance did not last. In the ninth minute Nacho Monreal went down in the corner of the box as Alireza Jahanbakhsh tried to stretch a leg around him to win the ball. The referee pointed to the spot, from which Aubemeyang fired the ball into the corner of the net. It was the Gabonese striker’s 20th league goal of the season, and there was plenty of time left for him to increase that tally.

But Arsenal slackened and the imbalances in their team became apparent. Sokratis Papastathopoulos earned himself a booking for a nonsensical dive near halfway in the 15th minute in what was a symptom of the drop in standards.

Brighton bucked up their ideas. And as so often, Arsenal’s defence looked vulnerable under pressure while their midfield failed to offer adequate protection.

At right-back Stephan Lichtsteiner, a 35-year-old making his first league start since February owing to the suspension of Ainsley Maitland-Niles, had trouble keeping up with Solly March.

Bernd Leno spawned jitters with erratic distribution, most alarmingly in the 26th minute when he kicked the ball straight to Jahanbakhsh at the edge of the box. In the pandemonium Shkodran Mustafi did well to block a shot by Murray before March clipped a cross back for the striker to try again from eight yards. Leno reacted sharply to stop his downward header.

Arsenal seldom control matches. But at least they carry a threat at the Emirates and they created chances to extend their lead. Mat Ryan had to parry a header from Mustafi following a corner in the 35th minute. Moments later the goalkeeper had to fling himself to his right to claw away a low shot by Aubemeyang after a cross from the right by Mesut Özil. And just before the conclusion of a damningly low-key first half Mkhitaryan raised the tone with a blast from 20 yards. Ryan batted it away.

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Whatever Emery said at half-time made no difference. Whether that is the manager’s fault is a matter of debate. His players continued to look disjointed and brittle. And the way they allowed Brighton back into the game was downright ridiculous, Xhaka slapping March on the shoulder as the attacker flew past him in the box. Murray sidefooted the penalty into the net.

Arsenal found urgency, at last, but could not locate the net. Brighton defended like tigers and, on one of the few occasions when Arsenal found a way past them, Aubameyang’s predatory instincts abandoned him when he shot wide from eight yards.

Emery made a triple substitution in pursuit of victory. His panicky team, meanwhile, seemed to be doing their best to throw away even the draw. Leno, at least, did well to save a header by Florin Andone before Gross’s miss.