Joe Kenton and Jason Oswell netted in the final 20 minutes to give Newtown another three points in the Welsh Premier League Conference play-offs.
The win secured the Robins place in the league and also tightened their grip on the end-of-season play-off places and another shot at Europe.
Throughout the game it was the Lilywhites who looked more likely to take the lead. However their chances came and went and that allowed Newtown to punish them late on.
Kenton notched his first for the club, before Oswell tapped home for his 18th goal of the season, 10 minutes from time.
Radnor Valley 1 Knighton
Division 2
Penybont 1 Llansantffraid Village 3