Javier Mascherano scored his first goal in 319 games for Barca from the penalty spot after Messi had been withdrawn.
As he ran up to take it, the Barca bench watched on in excitement, with Luis Suarez – rested for the match – barely able to contain his glee.
“At first I tried to get out of it but under pressure from my team-mates and the crowd I decided to take it on,” Mascherano said.
“It would have been a fun moment to remember in years to come had I missed it. I wasn’t sure about it at all but it was difficult to say no to my team-mates.”
It was the 32-year-old’s third goal in senior club football, having scored twice during three years at previous club Liverpool – who he left for Barca in 2010.
“The fans behind the goal were chanting for Mascherano to take it,” manager Luis Enrique said. “I am happy for him – he is a key player for the club and he has shown that down the years.”