Corinthians 2s lost on Sunday in a hard-fought game.
The first half ended scoreless with both teams having chances to score. Monkstown took the lead early in the second half after pinning the reds in their half for a sustained period.
Despite having plenty of possession and a number of short corners the Reds couldn't find the net and Monkstown got a second to seal the win with a back post deflection.
Ross McWilliam battled well in midfield with Colm Blennerhasett making a rare appearance.