British light heavyweight Buatsi earned a win yet unimpressive start to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a close ten-round contest at the Co-op Live Arena.
But the challenger had his moments, landing some telling clean blows in a fight where the approaches failed to mesh, with constant grabbing disrupting the action.
The scoring judges judged it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my finest performance but how do champions respond? They win," Buatsi stated in the ringside as he was met by disapproval from the spectators.
The Londoner got back to winning after his initial pro loss - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts believed the challenger, thirty-one, deserved the victory but the Derbyshire fighter experienced the second loss of his 28-bout professional journey.
The Champion Claims Win in Slow Affair
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to realize his potential - maybe in what feels like a last chance - under new promotional backing.
He started carefully, with neither fighter willing to take risks in a tentative early stages.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after damaging his hand during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who utilized a protective stance to narrowly win the cleaner periods.
The spectators' acceptance decreased during frequent holding, with the challenger going down several times during close exchanges.
Parker finished the stronger, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Hatton Tribute Motivates Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester contest to secure the European light-heavyweight title.
The stadium grew hushed for a profoundly moving homage before the fight as 10 bells tolled in memory of local hero Hatton, who died aged 46 in recently.
It was the premier televised boxing event in the city since the passing of Hatton. As the final chime ended, the quiet gave way to a roar of "there's only one Ricky Hatton".
The fighting inside the ropes reflected the emotion. The eventual winner was knocked down by a significant blow squarely on the face in the initial stage, standing uncertainly to his footing on the eight count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was injured quickly, significant bruising developing under his face as the pair landed hard punches.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the action hardly diminished over 12 rounds.
The victor barely secured the decision with official scores of even score, close margin and 115-112, but both fighters were persistent and brave, everything their inspiration Hatton stood for.
