Katlego Mphela slotted a 76th minute penalty for Amakhosi to claim the three points at Mbombela Stadium.
However, it was a forgettable evening for Stuart Baxter's men as the Brazilians thumped SuperSport United 3-0 to win the League with a game to spare.
The Glamour Boys dictated the flow of play in their tie, but their passing in the attacking third repeatedly let them down.
Tuks looked to soak up the early pressure and hit on the counter-attack, and it was they who had the first shot on goal in the 21st minute. It was not a dangerous effort from Junior Sibande, however, who shot well over from range.
Tuks, though, were virtually non-existent in attack and Itumeleng Khune had very little to do between the sticks for Amakhosi.
Chiefs finally began turning their pressure into goal-scoring chances on the half-hour mark.
Initially, Siphiwe Tshabalala saw one of his trademark corners almost sneak under the crossbar, but Washington Arubi managed to get a hand to it. The ball fell to Mphela, but he headed wide from only a couple of yards out when he should have scored.
Four minutes later Tshabalala was the creator once more when a free-kick from the right side of the field found Tefu Mashamaite unmarked ten-yards out, but he headed straight at the keeper.
Chiefs fashioned another glorious scoring chance two minutes before the break when a long throw-in into the box by Tsepo Masilela was flicked into the path of Bernard Parker, but he headed wide from close range.
The second half was more of the same from Chiefs, but they finally made their pressure tell late on when they were awarded a penalty after Kgotso Moleko was brought down inside the box by Sibande.
'Killer' stepped up and made no mistake from the spot, but the goal brought little reward as Downs later marched to honours in Tshwane.