Di Matteo barked: "United came here, we had two sent off and they scored an offside winner. That's a big advantage for the opposition.
"We're still playing well and creating chances. We need to be a bit more clinical, to take our chances and finish the game off."
The Italian maintained his side were too good to suffer another bout of the winter blues, which has cost them dearly in three of the last four seasons.
"We're in much better shape than in previous years, in a much better position, and very close to our best," he said.
"If we had won today, it would have been great for us.
"We're still in the mix. But the amount of games you play in this period has some kind of effect."