British light-heavyweight Buatsi earned a win yet disappointing start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a tight 10-round fight at the boxing arena.
But the challenger landed significant shots, connecting with powerful single shots in a match where the styles failed to mesh, with constant grabbing spoiling the contest.
Two judges scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my finest showing but how do champions respond? They win," the victor stated in the ring as he was met by disapproval from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Various analysts thought the challenger, thirty-one, deserved the victory but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
The Champion Claims Triumph in Dull Match
The fighter's advancement has stalled in recent times through promotional disputes and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now stands trying to realize his potential - maybe in what appears to be a last chance - under recent support.
He opened tentatively, with the two boxers prepared to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who worked behind a solid defense to edge the more effective stanzas.
The spectators' acceptance wore thin during regular grabbing, with the challenger going down several times during clinches.
Parker finished the stronger, but several stanzas were hard to judge. Although, ex-champion Carl Frampton - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the presence of hard hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Tribute Fuels All-Manchester Battle
In the secondary fight, Arthur beat Rea by split-decision in a excellent local rivalry fight to capture the continental championship.
The venue became quiet for a extremely emotional homage prior to the bout as a bell ceremony sounded in honor of the city's native Hatton, who succumbed aged 46 in recently.
It was the first major televised fight night in the urban center since the passing of Hatton. As the concluding sound disappeared, the stillness became a chant of "there's only one Ricky Hatton".
The fighting during the bout matched the sentiment. Arthur was knocked down by a powerful punch squarely on the jaw in the initial stage, standing uncertainly to his position on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, the opponent - in competitive blue - was injured early, noticeable damage developing under his orbital area as the duo landed powerful shots.
Rea, 27, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over the full distance.
The victor barely secured the result with judges scorecards of 114-114, close margin and clearer margin, but both fighters were determined and full of heart, all the qualities their inspiration Hatton stood for.
