The Poppies took an early lead through Liam Canavan against the Evo-Stik Northern Premier League Division One South side.
But Witton levelled on the stroke of half-time through Robert Hopley and then secured a 2-1 victory in dramatic fashion thanks to Wes Benjamin’s strike in the seventh minute of stoppage-time.
It was the latest example of the inconsistent form the Poppies have shown this season after they had won 7-0 at St Ives Town in the Evo-Stik Southern League Premier Division just seven days earlier.
And Law didn’t have many complaints as he conceded Witton’s “endeavour” proved too much for his own players to handle.
“We started really well and we were the better team,” the Poppies boss said.
“We were able to dictate the play and we got the goal after some good wing play and a decent finish.
“But we seemed to lose a grip on the game, mainly because of Witton’s endeavour, they just seemed to want it a bit more.
“We were unable to respond to the want and willingness, they won all the second balls.
“They scored just before half-time from a set-piece where we haven’t reacted to the second ball.
“The second half was much the same story. They had a lot more endeavour, they wanted it more than our players and it became a case of trying to see the game out and bring them back to Latimer Park.
“But we have been done in the seventh minute of stoppage-time and it has come from another set-piece where we haven’t won the second ball and their lad has, in fairness, produced an excellent finish.
“We were unable to keep ourselves in a game that we looked like we were going to control at the very start of it. It is a bitter pill and very, very disappointing.”
The Poppies, meanwhile, look set to have a departure from their squad with Ben Stephens expected to sign for Stratford Town following a seven-day approach.
Kettering return to Southern League action on Tuesday night when they head to Kings Langley.