Ards boss Niall Currie admitted that he should have substituted Craig McMillen before he was sent off in Saturday's disappointing stalemate with Donegal Celtic.
The Red and Blues drew 1-1 with struggling DC in a heated encounter at Clandeboye Park.
Former Hoops winger Gary Warwick gave Ards the lead in the sixth minute after he nudged home an Owain Beggs cross, but that was as good as things got for Currie's men, who wasted a host of chances to extend their advantage before eventually being made to pay.
In the 64th minute, left-back McMillen received a second yellow card, ruling him out of Friday's Steel & Sons Cup semi-final against Carrick Rangers at Seaview.
Within six minutes of his dismissal, Celtic were back on level terms, centre-back Danny Wallace heading home from six yards following a corner delivery.
The visitors were also reduced to 10 men in the 86th minute when Emmet Templeton received a straight red card for foul and abusive language, but Ards were unable to find a winner despite applying some decent pressure in the closing exchanges.
"I'm really disappointed," said a clearly frustrated Currie afterwards.
"We missed some great chances in the first half, we had four or five great chances to make it 2-0 and we didn't take them.
"I said to the boys at half time that you're only a set-piece or a deflection away from losing the points.
"I have to put my hands up and admit that I should have taken Craig McMillen off.
"He had been warned and warned about persistent fouling. We talked to him at half time and he seemed to be calm, but I should have taken the decision out of his hands. It ended up costing us."
Ards remain in second place in Belfast Telegraph Championship 1 but they are six points behind league leaders Bangor, who were not involved in any action this weekend.
Larne moved into third with an impressive 2-0 win over Knockbreda.
Striker Ciaran Murray scored both goals in the first half, the opener a particularly fine finish with his second coming from the penalty spot.
Harland & Wolff Welders claimed an exciting 4-3 victory over Ballyclare Comrades.
Joel Cooper had given Ballyclare the lead but the hosts raced into a 3-1 advantage thanks to a double from Michael McLellan and an additional strike by David Rainey, while Willie Armstrong missed a penalty.
Chris Trussell's quick-fire brace looked to have earned Comrades a point only for McLellan to complete his hat-trick with an 85th-minute winner.
Loughgall and Carrick Rangers played out a 1-1 draw at Lakeview. Kyle Cherry scored for Carrick, who are 10 points behind Bangor with three games in hand.
In Championship Two, meanwhile, Lurgan Celtic climbed to the top of the table with a 4-3 win over Limavady United at The Showgrounds. Sport & Leisure Swifts also won 4-3 away from home as they got the better of promotion hopefuls Annagh United.
At the other end of the table, relegation threatened duo Coagh United and Tobermore played out a 2-2 draw.