Three goals in the first half and a fourth late on from the Korean side meant a Percy Tau scorcher proved to be nothing more than a consolation, as Sundowns finished in 6th place at the club world championships in Japan.
Jeonbuk took control of proceedings from the onset, and found the opener through Kim Bokyung, who hit the roof of the net after getting on the end of a cross from the left flank in the 18th minute.
Jongho Lee then doubled the lead 11 minutes later, when a training-ground set-piece drill from outside the box allowed the 24-year-old forward to fire home from close range.
Ricardo Nascimento's night went from bad to worse when he scored an own-goal after an attempted clearance from a Jang Yunho cross, once again exposing Sundowns' poor defensive organisation with a counter-attack.
Jeonbuk goalkeeper Hong Jungnam went into thre break untested, as the likes of Khama Billiat, Keagan Dolly, Leonardo Castro and Percy Tau were starved of the ball by the Korean outfit's resolute and disciplined defensive structure.
A half-time change saw Sibusiso Vilakazi come on in place of Castro, as Pitso Mosimane looked to use a different approach in the second half.
Tau then pulled one back three minutes after the restart, after being played in behind the Jeonbuk defense by Thapelo Morena, before the 22-year-old rising star cut inside and sent a left-footed curler into the top left corner.
The Brazilians looked a much better composed and organised outfit in the second stanza, as they enjoyed some good passages of play in the attacking half.
However, Jeonbuk could have grabbed a fourth in the 59th minute, when Onyango was lefted stranded, but Wayne Arendse popped up with a crucial block to save his goalkeeper's blushes.
The Green Warriors eventually restored their three-goal cushion when Onyango came off his line and misjudged the flight of the ball, allowing substitute Shinwook Kim to head home in the 89th minute.
Mamelodi Sundowns: Onyango, Morena (Mohomi 81'), Nascimento, Arendse, Langerman, Kekana (c), Mabunda, Dolly, Billiat (Mbekile 75'), Tau, Castro (Vilakazi 46')
Jeonbuk Hyundai: Jungnam, Kyowon, Jongho (Kim 79'), Bokyung, Jongeun, Jaesung, Mooyeol (Leonardo 62'), Wonjae, Chulsoon (c), Youngchan, Yunho (Hando 72')