British light-heavyweight Buatsi secured a victory yet disappointing debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a competitive ten-round fight at the Manchester venue.
But Parker had his moments, delivering effective single shots in a contest where the styles never quite clicked, with excessive holding spoiling the contest.
The scoring judges scored it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They win," the victor commented in the arena as he was greeted with disapproval from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, merited the win but the British boxer endured the second loss of his 28-bout professional journey.
The Champion Earns Triumph in Dull Encounter
His career development has stalled in the past few years through contract problems and long spells of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors willing to be aggressive in a calculated early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand during the bout, was competing in only his second fight at light heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who operated with a protective stance to narrowly win the more effective stanzas.
The audience's tolerance diminished amid regular grabbing, with the challenger falling to the floor several times during clinches.
Parker ended stronger, but multiple periods were challenging to assess. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Russian star Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Homage Inspires Local Rivalry Battle
In the supporting bout, Lyndon Arthur defeated Rea by split-decision in a outstanding Manchester vs Manchester battle to secure the European light-heavyweight championship.
The arena became quiet for a deeply poignant memorial prior to the bout as ten bells sounded in remembrance of Manchester's own Ricky Hatton, who passed away at age 46 in recently.
It was the first major televised match card in the urban center since Hatton's passing. As the last bell disappeared, the silence transitioned to a roar of "there's only one Hatton".
The competition during the bout reflected the feeling. Arthur was sent to the canvas by a powerful punch squarely on the face in the early round, getting up unsteadily to his footing on the count of eight.
But the Manchester United-red attire of Arthur soon pressed ahead again. On the opposite side, Rea - in competitive blue - was injured quickly, heavy swelling developing under his face as the duo exchanged powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the pace seldom decreased over 12 rounds.
The victor barely secured the verdict with scoring tallies of 114-114, narrow lead and wider gap, but each competitor were persistent and courageous, exactly what their idol Hatton represented.
