British light-heavyweight Buatsi made a winning yet disappointing beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a close 10-round bout at the Manchester venue.
But the challenger found success, connecting with powerful individual punches in a match where the styles never quite clicked, with constant grabbing marring the action.
Two judges had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They prevail," Buatsi said in the ringside as he was faced disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Some ringside observers felt the challenger, 31, deserved the victory but the Derbyshire fighter endured the second setback of his 28-match career.
The Champion Secures Triumph in Uneventful Match
His career development has plateaued in recent years through management issues and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now finds himself trying to realize his potential - perhaps in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second appearance at light heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who operated with a tight guard to narrowly win the cleaner periods.
The crowd's patience decreased because of frequent holding, with Parker slipping to the canvas various instances during clinches.
The underdog closed well, but several stanzas were difficult to score. However, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Memorial Fuels Local Rivalry Fight
In the co-main event, Arthur overcame Bradley Rea by split-decision in a excellent all-Manchester battle to capture the European light heavyweight belt.
The stadium fell silent for a profoundly moving homage prior to the bout as ten bells tolled in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in recently.
It was the premier televised boxing event in the city since Hatton's death. As the concluding sound disappeared, the silence gave way to a shout of "there's only one Ricky Hatton".
The fighting within the ring equaled the feeling. The eventual winner was knocked down by a significant blow squarely on the face in the early round, getting up unsteadily to his position on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured soon, noticeable damage appearing under his orbital area as the duo exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the intensity rarely dropped over twelve rounds.
Arthur edged the verdict with scoring tallies of 114-114, 115-113 and clearer margin, but each competitor were determined and full of heart, all the qualities their idol the legend represented.
