British light heavyweight Buatsi secured a victory yet disappointing start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a close ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful clean blows in a match where the approaches didn't complement each other, with constant grabbing spoiling the action.
Two judges had it 96-94 to the winner, with the third a 95-95.
"It wasn't my greatest showing but how do champions respond? They prevail," the victor said in the arena as he was faced disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers believed Parker, thirty-one, deserved the win but the British boxer suffered the second defeat of his 28-bout professional journey.
Buatsi Claims Triumph in Slow Encounter
Buatsi's progress has stalled in recent years through management issues and extended periods of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to achieve expectations - maybe in what feels like a last chance - under recent support.
He opened tentatively, with the two boxers ready to overcommit in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for Buatsi, who operated with a solid defense to barely take the cleaner stanzas.
The crowd's patience decreased because of regular grabbing, with the challenger slipping to the canvas various instances during grappling.
Parker ended stronger, but multiple periods were hard to judge. Although, ex-champion the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Fight
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a terrific all-Manchester contest to capture the European light heavyweight championship.
The stadium became quiet for a extremely emotional tribute ahead of the contest as ten bells sounded in remembrance of Manchester's own Hatton, who died aged 46 in recently.
It was the premier televised match card in the city since Hatton's passing. As the concluding sound disappeared, the silence transitioned to a roar of "only one Hatton".
The competition inside the ropes equaled the emotion. The eventual winner was knocked down by a significant blow squarely on the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the traditional red attire of the fighter soon advanced again. Across the ring, the opponent - in opposing blue - was damaged quickly, heavy swelling forming under his eye as the fighters traded hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur barely secured the result with scoring tallies of draw, narrow lead and clearer margin, but the two athletes were relentless and full of heart, exactly what their inspiration the legend represented.
