The 32-year-old Namibian, who moves to 20-0(10 KOs), was awarded the bout 115-113 116-112 116-112 on the cards.
He was on the front foot from the start while Pungluang seemed willing to trade with him, throwing plenty of shots to the body.
However Ambunda did not tire and was comfortably ahead after dominating the 11th round.
That caused Pungluang, who won the title in Manila from AJ Banal, to attack in the final round: a succession of hooks and uppercuts rocked his opponent, but he was unable to put him on the canvas.
It is only the Thai's second defeat and brings to an end a 20-fight winning streak. He lost on split decision to Stephane Jamoye in 2009 and is now 43-2(28 KOs).
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