Leyton Orient boss Russell Slade admitted his side needed to be at the top of their game to take the three points from Coventry City as they kept the pressure on Sky Bet League 1 leaders Brentford.
After dominating the game, Orient had to wait until the 55th minute before Dean Cox was able to put them ahead. The midfielder latched on to a loose ball following a corner to drive the ball into the net form 12 yards.
Kevin Lisbie had wasted a golden opportunity just a minute earlier when he saw his penalty saved by visiting goalkeeper Joe Murphy after Andy Webster's foul on Cox, but Mooney settled the outcome 10 minutes from time.
He had only been on the pitch for four minutes when he saw his 20-yard shot escape the clutches of Murphy to seal the points for the home side.
"Coventry are a very, very good side and we needed to be on our best form," said Slade.
"They still have a chance of the Play-Offs and if they hadn't had their points deduction, they would be right up there.
"Their manager is doing a fantastic job for them and they pushed us all the way.
"Our attitude was excellent and the fact that we are absolutely relentless in everything we do paid off for us in the end.
"We had to keep knocking on the door and eventually we found a way through.
"It was a great strike from Dean Cox that took the pressure off us and so often, the first goal is so important and so it proved again.
"Our intensity throughout the game was so strong. Their keeper will be slightly disappointed with David Mooney's goal, but for Dave to get on target on his first game back was excellent.
"Our keeper was called upon three times in the second period and he rose to the occasion each time.
"His powers of concentration are excellent. We are doing everything we possibly can and nobody can ask for any more."
Sky Blues boss Steven Pressley admitted he is looking for new faces to bring to his squad.
"The players are working so hard for each other just now, but the problem is that we need to get certain personnel in," he said.
"I think that performance was crying out for strikers and I'm working hard to help this group out because they have given me everything.
"Even at one-nil, we had several good chances that brought some good saves from their goalkeeper.
"When you go from having the two top strikers in the league to having no strikers, it is very difficult. But I'm not making excuses, I have to find a way and get players in.
"Because of the injury to Callum Wilson and the Leon Clarke situation and, for me, his failure to support this group just now, we find ourselves with no real strikers available
"We are working morning, noon and night to get strikers in but it's very difficult to get the right players in.
"There are certain things that I'm not happy about but I couldn't ask for anymore from these players.
"Full credit to Russell Slade, of any of the side's up there, I would like to see Leyton Orient get promotion.
"They work ever so hard and Russell has built everything there that, in my opinion, a football club should be."