British light heavyweight Buatsi earned a win yet unimpressive debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a majority decision in a tight ten-round contest at the Co-op Live Arena.
But the challenger found success, delivering effective clean blows in a match where the techniques failed to mesh, with constant grabbing spoiling the contest.
The scoring judges judged it 96-94 for to the winner, with the third a even score.
"It wasn't my finest showing but what do champions do? They prevail," Buatsi commented in the ring as he was greeted with disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Some ringside observers thought the challenger, 31, merited the decision but the British boxer experienced the second defeat of his 28-bout career.
The Champion Earns Victory in Dull Affair
Buatsi's progress has slowed in recent times through management issues and long spells of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury in the contest, was making just his second fight at light heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who worked behind a protective stance to edge the cleaner stanzas.
The spectators' acceptance decreased because of constant clinching, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. However, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Battle
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a excellent Manchester vs Manchester battle to win the continental championship.
The venue grew hushed for a extremely emotional memorial prior to the bout as ten bells tolled in memory of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the premier televised match card in the urban center since Hatton's passing. As the final chime faded, the quiet transitioned to a chant of "there's just one Ricky Hatton".
The fighting inside the ropes reflected the emotion. Arthur was sent to the canvas by a significant blow directly to the face in the early round, rising shakily to his footing on the eight count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was marked up soon, noticeable damage developing under his face as the duo traded hard punches.
Rea, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor narrowly won the verdict with judges scorecards of 114-114, 115-113 and wider gap, but both fighters were determined and courageous, everything their idol Hatton stood for.
