After two recent defeats, at Penrhyncoch with only 10 men travelling and at Caersws last week, the Reserves were looking to bounce back.
The game started brilliantly when Dan Morgan put Llanfair ahead after 13 minutes.
The visitors equalised right before half time through Jack Thomas.
A dramatic end to the game saw Llanfair's goalkeeper Jack Roberts sent off for pushing over an opponent in the 77th minute.
However, with 10 men, it was Llanfair who won the game, with Karl Seliaerts' 92nd minute winner.
Next Fixture: Llandrindod (H) Sunday 8th May 2.30pm League
Player of the Match: Callum Evans