Kettering suffered their fifth defeat in eight matches as goals from Danny Thomas and substitute Iyseden Christie gave Tamworth a comfortable victory.
The Lambs' Daniel Bradley had a shot saved by Laurie Walker, before Thomas put the visitors ahead with a fierce left-footed strike from 20 yards.
Walker tipped over Kieron St Aimie's effort, but Christie sealed the win with a low shot after a Thomas pass.
Kettering's best chance fell to Leon McKenzie but his header went wide.
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Kettering Town manager Mark Stimson told BBC Radio Northampton:
"It's very frustrating because I thought we started the game on the front foot.
"We may have Adam Cunnington up front, and Moses Ashikodi and JP Marna with a bit of pace, but you don't have to hit it long every time.
"But it's a long season, we've got to make sure the boys keep working as a team - it's no good playing as individuals. They've got to take that on board.