British light heavyweight Buatsi made a winning yet disappointing debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a close 10-round contest at the boxing arena.
But Parker landed significant shots, delivering effective clean blows in a fight where the techniques didn't complement each other, with excessive holding disrupting the action.
The officials scored it 96-94 for to the winner, with the third a even score.
"It wasn't my finest showing but what defines champions? They succeed," Buatsi stated in the arena as he was greeted with disapproval from the crowd.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts thought Parker, thirty-one, deserved the victory but the British boxer endured the second setback of his 28-bout professional journey.
Buatsi Secures Triumph in Dull Affair
His career development has stalled in the past few years through management issues and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to achieve expectations - possibly in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers prepared to overcommit in a calculated opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was participating in his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who utilized a tight guard to barely take the cleaner stanzas.
The spectators' acceptance wore thin during constant clinching, with Parker falling to the floor multiple occasions during grappling.
The underdog closed well, but several stanzas were difficult to score. However, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Battle
In the supporting bout, Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to win the European light heavyweight title.
The venue grew hushed for a extremely emotional homage ahead of the contest as a bell ceremony rang in honor of local hero 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 silence transitioned to a chant of "there's just one Ricky Hatton".
The action inside the ropes reflected the sentiment. Arthur was floored by a powerful punch flush on the face in the initial stage, rising shakily to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was damaged soon, significant bruising appearing under his orbital area as the pair landed punishing blows.
Rea, 27, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the action rarely dropped over the full distance.
Arthur barely secured the verdict with official scores of even score, 115-113 and wider gap, but the two athletes were persistent and brave, everything their idol the legend represented.
