British light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a close ten-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective single shots in a fight where the styles never quite clicked, with frequent clinching spoiling the action.
Two judges scored it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my greatest showing but what defines champions? They win," the victor stated in the ring as he was greeted with disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers thought the challenger, 31, should have been awarded the win but the contender endured the second loss of his 28-fight professional journey.
The Champion Earns Victory in Dull Match
The fighter's advancement has slowed in recent years through contract problems and long spells of inactivity.
Previously predicted as the next star of British boxing, he now is positioned trying to achieve expectations - perhaps in what feels like a last chance - under recent support.
He opened tentatively, with the two boxers willing to overcommit in a cagey initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was participating in his second fight at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for Buatsi, who operated with a protective stance to barely take the better rounds.
The crowd's patience diminished during frequent holding, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker ended stronger, but many rounds were hard to judge. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Hatton Tribute Motivates Manchester Derby Battle
In the co-main event, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry contest to win the European light-heavyweight championship.
The arena became quiet for a deeply poignant memorial prior to the bout as a bell ceremony rang in honor of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the concluding sound ended, the stillness became a roar of "there's only one Ricky Hatton".
The action inside the ropes matched the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the face in the second round, getting up unsteadily to his position on the referee's count.
But the traditional red equipment of Arthur soon pressed ahead again. From the other corner, the opponent - in opposing blue - was injured quickly, significant bruising developing under his orbital area as the pair traded powerful shots.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over the full distance.
The victor narrowly won the verdict with judges scorecards of even score, close margin and 115-112, but the two athletes were determined and courageous, everything their inspiration Hatton embodied.
