British light heavyweight Buatsi earned a win yet underwhelming debut to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight ten-round fight at the Manchester venue.
But the challenger had his moments, delivering effective individual punches in a match where the techniques never quite clicked, with excessive holding marring the action.
The officials scored it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my best performance but what do champions do? They win," Buatsi said in the ring as he was met by negative reactions from the audience.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Various analysts felt the challenger, thirty-one, should have been awarded the victory but the British boxer experienced the second loss of his 28-fight professional journey.
The Champion Earns Victory in Dull Affair
His career development has plateaued in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to achieve expectations - perhaps in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to take risks in a calculated initial rounds.
The challenger, whose sole prior loss came at super-middleweight 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, the underdog had stayed in contention, making life awkward for the favorite, who operated with a tight guard to barely take the better periods.
The spectators' acceptance decreased amid constant clinching, with the challenger slipping to the canvas various instances during grappling.
The underdog closed well, but many rounds were hard to judge. Although, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires Manchester Derby Contest
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a outstanding local rivalry fight to win the continental belt.
The arena grew hushed for a extremely emotional homage before the fight as 10 bells tolled in honor of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised match card in the city since Hatton's passing. As the final chime faded, the silence transitioned to a shout of "there's only one Hatton".
The action inside the ropes matched the sentiment. The eventual winner was floored by a powerful punch directly to the jaw in the early round, rising shakily to his footing on the referee's count.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was damaged soon, significant bruising forming under his face as the duo exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action rarely dropped over 12 rounds.
Arthur narrowly won the decision with official scores of draw, 115-113 and wider gap, but the two athletes were persistent and brave, all the qualities their inspiration Hatton embodied.
