It's also Sunderland's first win over Joey Barton as a manager, ticking off another of their voodoos in what is shaping into an excellent season.
Chances were few and far between, with no player on either side really covering themselves in glory. O'Brien's finish was a moment of rare quality in a pretty dire affair.
Story of the game
Zain Westbrooke had the first chance of the game. A smart passage of play from the hosts found him just outside the penalty area, he was able to get a yard of space away from Josh Scowen and get a low effort away on his weaker left foot. It skidded across the turf just wide and Lee Burge probably had it covered.
There was no rhythm to the game, the ball was spending a lot of time in the air and neither team was able to settle on the ball for very long.
Sunderland's best chance of the opening 15 minutes fell to Aiden McGeady on the edge of the box. Liam Leahy wanted too much time on the ball and was robbed by Lyndon Gooch down the right of the Rovers penalty area. He went down looking for a penalty under minimal contact, the referee didn't even bat an eyelid.
Carl Winchester was there to collect and feed the ball to McGeady, it got stuck under his feet and he couldn't sort them out and had to hook it towards the top left hand corner but his angles were wrong and he skewed it over the bar.
Joey Barton had clearly got his player fired up as they were the better of the two sides. Dion Sanderson nearly gifted them a clear opening. The Wolverhampton Wanderers loanee tried to control the ball and lost out to Jonah Ayunga. He had more time than he probably realised, taking a couple of touches and lashing a fierce effort just wide of Burge's post. He was baring down on goal and maybe could have taken a couple more touches to make it a direct one on one with the Sunderland ‘keeper.
Sunderland started to assert themselves on the game after that, seeing more of the ball without forcing Anssi Jaakkola into a save of any kind.
The best chance they created before the half hour was an Aiden O'Brien header from a well worked corner. The Sunderland players gathered on the edge of the box waiting for the signal from Lyndon Gooch. He gave the signal but then stuttered before kicking, by that point the likes of Charlie Wyke and Sanderson were marked. The corner was well flighted, finding the head of O'Brien but it flew harmlessly wide.
Just after the half hour Sunderland started to open up their hosts. Firstly a freekick just outside the box on the left was taken quickly, Rovers had switched off allowing Gooch a one on one from an angle. His low effort was well parried by Jaakola up into the air so that Wyke on the rebound couldn't direct his header towards goal.
McGeady then found some space, a couple of feints inside the box gave him a shot on his right but his shot was quickly charged down by a defender away from danger.
Sunderland did finally get the breakthrough after 39 minutes. Good play down Sunderland's right had found Wyke in the penalty area, he tried to lay it off for O'Brien towards the byline but Lahey stuck a foot in to get it out for a corner.
From the resulting corner Max Power floated the ball in, and despite all the hussle and bussle in the box, Aiden O'Brien was still able to ghost in past defenders and side foot the ball into the bottom left corner in a calm fashion that had been lacking up to that point in the half.
At the half Lee Johnson will have been relieved. His side had been well under par for sustained period's of the first period and yet still found themselves in the lead. For Joey Barton, his players had executed the gameplan well. It had been a scrappy game and until the goal they had shaded the chances.
Into the second half and it was another slow start by both sides. Rovers continued to make it scrappy, not letting Sunderland build up a rhythm. To counter them, Sunderland were trying to go direct, managing two or three passes before losing the ball.
A better team would have been able to counter and punish Sunderland, but the hosts looked a team devoid of confidence. They were leaving bodies behind the ball, not committing the bodies necessary to put Sunderland in trouble.
It took 20 minutes for Sunderland's first sustained spell of possession. It ended with Gooch being crowded out on the right hand side of the box. He laid the ball off towards Power by the byline. He floated a deep cross in, finding McGeady at the far post, the former Republic of Ireland international couldn't decide between going with his head or his foot and in the end hooked it over the bar.
It had woke Sunderland up and they started to twist the screw on their hosts. Bristol Rovers were being opened up with ease and Sunderland should have doubled their lead.
McGeady was starting to get on the ball more popping up on both flanks. This time he was on his more favourable left. He left the fullback bamboozled before cutting back to the edge of the box where goalscorer O'Brien was lurking. It looked like being a case of simply sweeping it into either corner from 12 yards. On it's way to him the ball bobbled before he hit it, meaning he got under it and blazed it over the bar.
Sunderland looked to be running out of steam, Rovers had slowed the tempo down and the chances had dried up. The only save Jaakkola had to make heading into the final ten minutes was from Charlie Wyke. A long ball by substitute Grant Leadbitter was well taken on his chest by Sunderland's number nine. He pinned the defender swiveling on the ball and releasing a low effort which the Finnish stopper had to get down quickly to stop.
McGeady then crashed a freekick off the post after 81 minutes as Sunderland looked to kill the game off. Jaakkola then made an excellent save from Wyke seconds later. Winchester burst into the box and was well tackled by former Sunderland defender Jack Baldwin. The ball fell to Wyke who fired a low effort through the legs of a defender. Unsighted the Rovers goalkeeper got down well with a strong hand to turn it round the post.
With it only being a one goal margin, the hosts were always in the game and they had a late flurry of chances.
First from a corner they caused chaos, the ball was bouncing around and fell to Josh Grant. He flicked an effort towards the near post and Burge had to be sharp to keep it out.
Seconds later they had another chance. A deep corner found David Tutonda around the back. He kept his header low but Burge did well to tip it wide.
Sunderland were camped in their half in the final few seconds but Rovers couldn't get the ball to stick long enough to create a clear chance and in the end when they reached the box, a class of heads between Ayunga and Luke O'Nein was enough to see Sunderland over the line.
Man of the Match - Anssi Jaakkola
Let’s call a spade a spade, neither side will want to rewatch that game anytime soon. It was dull, slow, devoid of any quality. For Sunderland it's a professional win by a narrow margin but it might have been more comfortable if it wasn't for Bristol Rovers goalkeeper Anssi Jaakkola.
He did well when called into action, making sure if he did have to parry Sunderland couldn't rebound it.
He couldn't have done anything about the goal but especially in the second half he made smart saves, specifically the one from Wyke when he had to get down low quick and have a strong hand to keep it out.