Lionel Messi didn't start but drew a roar from the crowd as big as any other on the night when he got up off the bench and started to warm up 20 minutes into the second half.
Ousmane Dembele and Andre Gomes also scored for the Spanish champions before Sibusiso Vilakazi replied for the hosts at Soccer City, near Johannesburg.
His every touch drew huge applause and Sundowns defender Wayne Arendse was beaming after the final whistle having exchanged shirts with the Argentine maestro.
But Barcelona are yet to confirm if the match will take place and many think they are unlikely to do so given that the La Liga season is not yet over. They surprised us a little bit because they were very fast.
The Spanish giants kept their end of the deal in fielding all their star players as they defeated the Absa Premiership champions in a Mandela Centenary Cup match on Wednesday.
Sundowns coach Pitso Mosimane said he was unable to speak on behalf of Barca.
"We did make crucial defensive errors, but I took a lot of positives from this match, including our passing and how we dispossessed Barcelona at times".
Barca goalkeeper Marc-Andr ter Stegen, meanwhile, added: "It has been a great experience for us and we are pleased to have won in front of the South African fans".
Substitute Andre Gomes scored Barcelona's third in the 66th minute, before Messi was introduced to a rousing reception by the South African supporters in the 70th minute.
There were nearly wholesome changes for the Barcelona in the second half as they continued to dominate the former Caf Champions League winners and a third goal arrived in the 66 minute.