Brown had only just come on last weekend when he collected a long pass from Toby Flood and immediately moved the ball wide to David Strettle, who crashed over the line in the final play of the game.
Strettle insisted he had grounded the ball under pressure from three Welsh defenders but television official Iain Ramage felt the footage was inconclusive and Wales won 19-12.
Brown immediately questioned whether he was at fault, whether he should have gone for the line himself or delayed his pass to draw one of the defenders.
O'Shea not only cleared Brown of any blame but believes the Harlequins full-back, who will start against Newcastle, is close to unseating Ben Foden as England's full-back.
"Browny texted me after the game and said 'should I have gone for it'? I said 'no you were right to give the ball'," said O'Shea.
"Browny could have had a go himself but he would have been tackled. If he had waited any longer to pass they'd have hit him.
"He did exactly what he needed to do and give the ball to Strettle.
"You can never give a wing, who is four yards from the line, the ball too early.
"The bottom line is he scored, it just wasn't given.
"Browny has worked really hard to get himself back in the England squad. It has been a massive wait (since 2008) and a battle and I am delighted he has done it.
"Hopefully, he will get a chance to start a game. I think he is getting closer.
"All he can do is come back this weekend, play hard, play well and ask the question.
"The good thing for England is you have someone putting the pressure on. It is not a fait accomplis."
Brown, Joe Marler and Jordan Turner-Hall have all been released by England to start for Harlequins in their top-versus-bottom showdown at Kingston Park.
"Joe is very confident and in a really good place. The fact he has been capped is a monkey off his back, you can see him relax more as a player and it will make him more dangerous," O'Shea said.
"It has been a big boost of confidence for those three boys."
Harlequins were beaten by Gloucester last weekend in a thrilling Premiership encounter but they earned what could be a precious losing bonus point at Kingsholm.
Quins will face a Newcastle side who are six points adrift at the bottom of the Premiership but battling hard for survival.
"You can ignore the fact it is first against 12th," O'Shea said.
"I know their coaching team well. It will be a monumental battle for us. They are scrapping for their lives but we are aiming for something this team absolutely craves.
"These are the games you have to put a performance in and we will not be outworked. Nick Easter has spoken as captain about the expectations.
"We have been top of the league since the third round, we have been there to be shot at and the guys keep reacting in the same way."
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