Messi came off the bench to a standing ovation.
Their unbeaten run was eventually ended following a 5-4 away loss to Levante in their penultimate league game of the season.
Insiders at the club said Messi is part of the package that was agreed to during the negotiations for the match and he will be in SA with superstars such as Samuel Umtiti, Philippe Coutinho‚ Ousmane Dembélé‚ Luis Suárez‚ Sergio Busquets‚ Gerard Piqué and Jordi Alba.
But there was to be no repeat of that result at the FNB Stadium, where the lively Dembele punished a poor defensive pass to open the scoring in the third minute, before Luis Suarez tucked home a second from inside the box 16 minutes later.
La Liga's newly crowned champions then doubled their lead on the 19th-minute mark after Suarez was put through in on goal to calmly slot the ball past Sundowns keeper Denis Masinde Onyango to make it 2-0.
Barcelona conclude their domestic campaign against Real Sociedad at the Nou Camp on Sunday.
According to Mundo Deportivo, Barca are on a tight schedule: they arrived in Johannesburg this morning, play Sundowns this evening, then fly back to Spain on tonight - so it really is a lightning visit.
Sundowns president Patrice Motsepe confirmed that his outfit will play hosts to the LaLiga champions just days after clinching their eighth PSL title.
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