UK light heavyweight Buatsi made a winning yet disappointing start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a tight ten-round fight at the Manchester venue.
But Parker had his moments, connecting with powerful individual punches in a contest where the techniques never quite clicked, with constant grabbing marring the fight.
The scoring judges had it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest showing but how do champions respond? They win," the victor said in the ringside as he was faced boos from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, deserved the win but the British boxer experienced the second loss of his 28-match professional journey.
Buatsi Claims Victory in Uneventful Affair
The fighter's advancement has stalled in the past few years through management issues and considerable time of lack of fights.
Once tipped as the future of British boxing, he now is positioned trying to fulfil that early promise - maybe in what seems like a last chance - under recent support.
He began cautiously, with neither fighter prepared to be aggressive in a calculated early stages.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a solid defense to narrowly win the more effective periods.
The crowd's patience wore thin amid frequent holding, with the challenger slipping to the canvas several times during grappling.
The underdog closed well, but several stanzas were difficult to score. However, former world champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor advances, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Contest
In the co-main event, Arthur overcame Rea by close verdict in a terrific all-Manchester contest to win the European light-heavyweight championship.
The venue became quiet for a profoundly moving memorial prior to the bout as 10 bells tolled in remembrance of local hero Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the final chime faded, the stillness gave way to a roar of "there's only one Ricky Hatton".
The competition during the bout reflected the emotion. The eventual winner was knocked down by a significant blow flush on the jaw in the second round, standing uncertainly to his feet on the referee's count.
But the traditional red shorts of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was injured quickly, noticeable damage forming under his eye as the pair landed punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur barely secured the result with official scores of 114-114, 115-113 and wider gap, but each competitor were persistent and brave, exactly what their idol the legend stood for.
