The Bay had two players controversially sent off for second yellow cards as they lost 2-1 at Boston United in the Skrill North.
The Seagulls led 1-0 at half-time with a penalty by Jonathan Royle on 43 minutes after Marc Williams had been brought down in the area by Boston goalkeeper Lewis King.
It was a lead the Bay deserved as they had played really well and dominated much of the half.
But referee Mike George changed the game when he gave Danny Taylor a second yellow for taking a free kick before he had blown his whistle.
That wrecked Bay’s concentration and Boston equalised almost immediately through Spencer Weir-Daley in a goal area scramble.
The Bay then had Tom Smyth also sent off , apparently for dissent after the referee awarded a harsh foul against him, and from the free-kick Carl Piergianni headed Boston’s winner with 11 minutes remaining.
The Bay also had coach Ade Akinbiyi ordered from the bench for remarks he made to the referee.
ColwynBay: Sanna, Taylor, Lea, Crowther, Smyth, Royle, Evans, Sean Williams, Hopley, Marc Williams, Darkwah. Subs: Joyce, Louis Moss, Ellison, Matthews, East.