Sale were penalised in the final two minutes of the Aviva Premiership encounter for a scrum offence when leading 19-18. Irish fly-half Adrian Jarvis, who had kicked an earlier penalty, stepped up and landed his second shot at goal, denying the Sharks victory.
The match had been close throughout the 80 minutes, with Sale's early 10-point lead courtesy of Rob Miller's converted try and Nick Macleod's penalty, wiped out by the break.
Macleod finished the game with four penalties to his name, while flanker Bryn Evans and wing Topsy Ojo went over for tries and rising star Tom Homer booted a penalty and conversion.
Diamond, though, was forthright in his views on Barnes, who he felt should not have penalised his side at the end for a scrum offence.
The Sharks' executive director of sport said: "I'm concerned about the referee being absolutely right about the penalty at the scrum.
"I'm not whinging but if the referee is going to make his interpretations, let it be consistent. That's what we are after.
"It is hard to take when such a crucial decision is made like that. He has to be 100 per cent right that we wheeled the scrum. He ought to come to a coaching session and see that the wheel went out of the game 10 years ago.
"The hardest thing as a coach is we didn't play to our full potential today and the responsibility is on the coaches, players and ourselves.
"But, within three minutes (at the end), we could have and should have won the game."
Diamond claimed that, as much as coaches try to talk to referees about the game, it is a "one way" conversation.
"There is a lot of dialogue but it is one way - from the coaches to them," said the former hooker. "All we want to see is them learning."
Irish head coach Toby Booth, meanwhile, called the scrum incident at the end a "stonewall" decision, saying that referee Barnes was correct.
And Booth was happy that Irish had laid to rest a horrible beating at Bath's Recreation Ground last weekend by winning this one.
"If we had been more clinical, we could have made it more comfortable," said Booth.
"That's what pressure does and that is what an injury list does. By the first 10 minutes, we were a bit tentative, and you have to give Sale credit for that.
"But we could have been considerably in front by half-time, if we had been more clinical. But I'm not going to shy away from the fact that the victory was very important from what we produced last week.
"The quality of your group is by how you respond in adversity and I thought they were absolutely outstanding in effort and intensity. We were good for it."
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