British light heavyweight Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But Parker found success, delivering effective clean blows in a match where the styles never quite clicked, with frequent clinching disrupting the contest.
Two judges judged it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi stated in the arena as he was greeted with disapproval from the spectators.
The Londoner bounced back after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th career victory.
Various analysts thought the challenger, thirty-one, deserved the win but the Derbyshire fighter suffered the second defeat of his 28-match career.
Buatsi's progress has stalled in the past few years through promotional disputes and long spells of lack of fights.
Once tipped as the rising talent of UK boxing, he now finds himself trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter willing to take risks in a tentative opening few rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a solid defense to edge the more effective stanzas.
The spectators' acceptance decreased during frequent holding, with the challenger falling to the floor several times during clinches.
Parker ended stronger, but multiple periods were hard to judge. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a terrific local rivalry battle to capture the continental title.
The arena became quiet for a extremely emotional homage before the fight as 10 bells sounded in remembrance of local hero Hatton, who succumbed aged 46 in September.
It was the premier televised boxing event in the location since Hatton's passing. As the last bell ended, the silence gave way to a roar of "there's just one Hatton".
The competition inside the ropes matched the sentiment. Arthur was floored by a left hook directly to the jaw in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored shorts of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was damaged soon, significant bruising forming under his orbital area as the fighters traded punishing blows.
Rea, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over 12 rounds.
Arthur barely secured the verdict with scoring tallies of even score, close margin and wider gap, but both fighters were determined and courageous, exactly what their idol Hatton embodied.
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