Pivotal moments crucial for Houston
Peter Houston described it as very much an "off-day" as Dundee United fell to a 3-1 defeat to Aberdeen at Pittodrie.
Skipper Jon Daly claimed his 21st goal of the season for the visitors but it wasn't enough as they suffered a first defeat in seven games and slipped a place to fifth in the table.
"It was an off-day but there were pivotal moments that could have changed the match," Houston admitted to BBC Scotland. "In the first half I thought we were denied a stonewall penalty and I just don't understand the reason the officials gave our players when they told them it was an accident.
"Secondly, Dusan Pernis, who has been great for us, made an uncharacteristic error in giving them a tap-in," he added. "I'm frustrated and annoyed and I know the players will be as well as we have set ourselves high standards because of the run we are on."