Manchester United headed for the break with a goal thanks to an 18th-minute goal from Robert Lewandowski.
The Polish striker converted from a spot kick to give Blaugrana the lead at Old Trafford.
David De Gea got the ball, but his shot was too strong to stop.
What angered and puzzled United fans was the way the penalty was awarded.
Bruno Fernandes, who missed a golden opportunity to give the Red Devils the lead, dabbled in Alejandro Barde, who started ahead of Jordi Alba.
The Barcelona star was treated gently at best before collapsing to the floor in agony at the slightest touch.
As a result, referee Clement Turpin awarded Barcelona a penalty.
Barcelona were awarded a penalty for this pull from Bruno Fernandes in Alejandro Barde’s arm.
Right decision or tough decision?
Let us know what you think 💬👇#BBCFootball #UEL #MUNBAR pic.twitter.com/vf4ffNEx6s
— Today’s game (@BBCMOTD) February 23, 2023
Do you agree with the penalty call to Bruno Fernandes? 🤔 pic.twitter.com/CqZjNWhoQj
— ESPN UK (@ESPNUK) February 23, 2023
The decision angered Eric ten Hag, and the Dutchman did not hide his disappointment and anger over the questionable call.
Turpin had to approach and warn the United boss, who had his arms crossed from the touchline.
Another dubious decision from Turpin came just minutes after Lewandowski slammed into the net.
A rising Luke Shaw was in front with the ball before being knocked down by Ronaldo Araujo on the edge of Barcelona’s box.
The referee decided there was no reason to stop play and simply waved and let the game go on.
The controversial decision comes after Jules Kunde’s first foul on Marcus Rashford at the Camp Nou. It looked like a missed scoring chance, but nothing was given to the Red Devils.
United fans know Turpin well. In his three matches for United with a Frenchman in charge, he is the only one the Reds have won. The most high-profile United match refereed by Turpin was the 2021 Europa League final loss to Villarreal.