British light-heavyweight Buatsi secured a victory yet unimpressive debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a split decision in a close 10-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful individual punches in a contest where the techniques failed to mesh, with excessive holding spoiling the action.
The officials scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest performance but what do champions do? They win," the victor stated in the arena as he was greeted with negative reactions from the spectators.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Various analysts thought Parker, thirty-one, merited the decision but the contender endured the second loss of his 28-fight professional journey.
The Champion Earns Win in Uneventful Encounter
Buatsi's progress has stalled in recent years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter ready to take risks in a cagey initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was making just his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who operated with a tight guard to barely take the cleaner periods.
The audience's tolerance wore thin during frequent holding, with Parker falling to the floor multiple occasions during clinches.
Parker ended stronger, but many rounds were difficult to score. However, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific Manchester vs Manchester battle to win the continental title.
The stadium fell silent for a profoundly moving homage prior to the bout as 10 bells rang in memory of local hero Hatton, who died aged 46 in recently.
It was the premier televised fight night in the urban center since Hatton's death. As the concluding sound ended, the silence transitioned to a roar of "only one Ricky Hatton".
The competition inside the ropes reflected the sentiment. The eventual winner was sent to the canvas by a significant blow squarely on the face in the second round, rising shakily to his footing on the count of eight.
But the traditional red shorts of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was injured early, noticeable damage appearing under his face as the pair exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the intensity rarely dropped over 12 rounds.
The victor barely secured the decision with scoring tallies of 114-114, 115-113 and 115-112, but each competitor were relentless and full of heart, everything their idol Hatton embodied.
