The new champions fielded six of the team that overcame Zamalek 3-1 on aggregate in the final of the African club competition.
The new champions fielded six of the team that overcame Zamalek of Egypt 3-1 on aggregate in the final of the premier African club competition.
A seventh starter in Alexandria last Sunday, Zimbabwean Khama Billiat, was introduced for the second half in place of injured Ivorian striker Yannick Zakri.
But it was Themba Zwane, an unused Champions League substitute, who came off the bench in Pretoria to swing the League Cup first round match in favour of the title-holders.
He created space for captain Hlompho Kekana to drill the ball past Zimbabwean goalkeeper George Chigova for the lead on 65 minutes.
Unmarked Zwane scored a simple second goal five minutes later at Lucas 'Masterpieces' Moripe Stadium, tapping in a low cross at the far post.
Sundowns are only the second South African champions to conquer Africa after Orlando Pirates, who triumphed in 1995 when the competition was called the African Cup of Champions Clubs.
"My boys are unbelievable professionals," said Pitso Mosimane, the first South African to coach a Champions League-winning team.
"They trained the day after becoming African champions and they had very little rest on the eve of this match due to celebratory events."
Sundowns host Cape Town City Sunday in the Premiership, where they have fallen five fixtures behind due to Champions League commitments.