Bukayo Saka missed a penalty against Real Madrid after trying to chip the ball with Thibaut Courtois pushing the ball away with ease.
It came after Arsenal were awarded an early penalty against Real Madrid at the Bernabeu after Raul Asencio hauled Mikel Merino down from a corner.
The decision needed VAR intervention, with the referee being sent to the pitchside monitor before making the call.
To loud whistles and jeers, Saka stepped up to take the spot-kick but his effort was disappointing.
Bukayo Saka missed a crucial penalty against Real Madrid
Reuters
Appearing to try the famous Panenka technique, the England international got it all wrong as his effort limply lifted off the ground.
Courtois had already dived but was still able to get a big paw to the ball before pushing it out for a corner, then cheering in front of the Real fans as his team-mates rejoiced.
If Saka had scored, it would have put Arsenal 4-0 up on aggregate and surely would have snuffed out any chance of a comeback.
The Gunners thrashed the European giants 3-0 at the Emirates last week but Real have remained confident that they can overturn the result.
Fans were left baffled by the forward, with one saying: "Bukayo what were you thinking?! Why change what you normally do?!"
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Another wrote: "That's one of the worst (on target) penalties I've seen. Soft, saveable height, not in the side netting. Will he regret that?"
While a third posted: "That penalty was far too easy and casual from Saka. Why the change, he normally thumps them in?"
And Arsenal legend Martin Keown was also critical, speaking to TNT Sports at half-time: "Bukayo Saka just gets it completely wrong. That was a massive opportunity to put this to bed."
It is the second missed penalty of Saka's career, having famously missed in the Euro final in 2021 when England lost to Italy at Wembley.
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Bukayo Saka attempted to chip his penalty to disastrous effect
Reuters
Matters went from bad to worse for the Gunners after Declan Rice conceded a penalty moments later, though VAR overturned the decision after sending the referee to the monitor again.
With a cross being lofted in, the midfielder was spotted in a tussle with Kylian Mbappe, who theatrically threw himself to the ground.
Rice protested angrily after the decision was given as he was shown a yellow card, though it appeared that this was rescinded.
After watching the incident again, the referee admitted his mistake - much to the disdain of the Bernabeu crowd.
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Bukayo Saka was consoled by his team-mates after missing a penalty
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It made for a feisty start to the match, with both sides looking to progress to the semi-final of the Champions League.
The winner of the tie will face Paris Saint-Germain, who beat Aston Villa 5-4 on aggregate on Tuesday following a true European classic.
After losing 3-1 to PSG last week, Villa found themselves 2-0 at home on Tuesday night.
However, they launched an incredible comeback of their own by netting three - though it was not enough to overturn the deficit as Luis Enrique's men made it through.
