British light-heavyweight Buatsi made a winning yet unimpressive debut to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a split decision in a close ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a fight where the approaches never quite clicked, with constant grabbing marring the fight.
Two judges had it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my finest display but how do champions respond? They succeed," the victor said in the ringside as he was greeted with disapproval from the spectators.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts thought Parker, thirty-one, deserved the decision but the contender suffered the second defeat of his 28-bout professional journey.
Buatsi Claims Triumph in Slow Match
His career development has stalled in recent times through promotional disputes and long spells of inactivity.
Once tipped as the future of British boxing, he now is positioned trying to fulfil that early promise - possibly in what seems like a last chance - under new promotional backing.
He opened tentatively, with both competitors willing to overcommit in a tentative early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who utilized a protective stance to edge the better stanzas.
The spectators' acceptance decreased amid constant clinching, with Parker slipping to the canvas several times during clinches.
The underdog finished the stronger, but multiple periods were difficult to score. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to secure the continental championship.
The venue grew hushed for a extremely emotional tribute ahead of the contest as ten bells sounded in memory of Manchester's own Hatton, who succumbed 46 years old in September.
It was the premier televised fight night in the urban center since Hatton's death. As the last bell ended, the silence became a chant of "there's only one Ricky Hatton".
The action during the bout matched the feeling. The eventual winner was knocked down by a left hook directly to the jaw in the early round, getting up unsteadily to his feet on the eight count.
But the red-colored shorts of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was injured early, significant bruising forming under his face as the duo exchanged powerful shots.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the pace hardly diminished over 12 rounds.
The victor edged the result with judges scorecards of 114-114, close margin and wider gap, but the two athletes were relentless and full of heart, all the qualities their idol the legend embodied.
