The Austrian defender used his weaker right foot to attempt a clearance, and the result was an equaliser for Barca
Friday's Champions League showdown between Bayern Munich and Barcelona started with a bang, as both teams scored inside the first seven minutes.
After Thomas Muller opened the scoring four minutes in, Barcelona found an equaliser three minutes later from an unlikely source: Bayern defender David Alaba.
The Austrian, normally so reliable, could only swipe at a cross from Jordi Alba, sending the ball looping over Manuel Neuer to level the quarter-final at 1-1.
The left-footed Alaba used his right foot in his attempted clearance, partially explaining its unintended outcome as the favoured German side were pegged back.
Alaba is usually a reliable performer for the Bundesliga champions, who are "cautiously optimistic" they will be able to tie the defender down to a new contract.
Just 14 minutes after Alaba's own goal, Bayern went back in front after Ivan Perisic struck to give his side the lead again. And in the 27th minute the lead was doubled as Serge Gnabry struck for Bayern, before Muller scored again to make it 4-1 in the 31st minute.
After a lightning-fast start to the match, there was plenty of reaction to Alaba's own goal.