SuperSport did the damage in the first half, as Jeremy Brockie bagged a brace to go with strikes from fellow forwards Bradley Grobler and Thabo Mnyamane.
Junior Mensah reduced the deficit shortly after the break at Lucas Moripe Stadium.
Matsatsantsa's progress in the competition depended on pool winners TP Mazembe beating Horoya 2-1 in a simultaneous fixture in Lubumbashi, DR Congo.
Mazembe finished with 12 points from six games - two points more than United, three ahead of Horoya, while Mounana failed to open their account.
In Tshwane, ex-Platinum Stars hitman Grobler drew first blood 13 minutes in with a diving header following a neat chip into the area by Aubrey Modiba.
Grobler threatened again midway through the stanza as he hoisted an effort over the bar from distance, minutes before strike partner Brockie steered a half-volley astray.
However, Mnyamane doubled the advantage with a tidy finish in the 27th minute after being released on goal by the influential Grobler.
Brockie made it 3-0 in the 34th minute from close range, having been teed up by veteran midfielder Reneilwe Letsholonyane in 'Yeye''s 300th start in topflight football.
Brockie struck again with a penalty, harshly awarded for a seemingly fair challenge on the New Zealander, on the stroke of half-time to notch up his 20th goal of the season.
The visitors showed more life after the interval, and pulled one back through Mensah in the 54th minute, but the hosts protected their comfortable lead to advance in the second-tier continental competition.
SuperSport: Williams, Kekana, Daniels, Mashamaite, Modiba, Letsholonyane (Alexander 60'), Furman, Phala, Mnyamane (Mokoena 60'), Brockie, Grobler (Bhasera 80').
Unused subs: Pieterse, Morton, Nkhatha.