British light heavyweight Buatsi made a winning yet unimpressive debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a tight 10-round contest at the boxing arena.
But the challenger landed significant shots, delivering effective individual punches in a fight where the approaches failed to mesh, with excessive holding disrupting the fight.
The scoring judges had it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what do champions do? They succeed," the victor commented in the ring as he was greeted with negative reactions from the audience.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Various analysts felt the challenger, thirty-one, deserved the win but the contender endured the second defeat of his 28-match professional journey.
Buatsi Claims Win in Uneventful Encounter
The fighter's advancement has slowed in the past few years through contract problems and considerable time of inactivity.
Earlier forecast as the future of the British fight scene, he now is positioned trying to realize his potential - possibly in what feels like a final roll of the dice - under recent support.
He began cautiously, with neither fighter willing to overcommit in a calculated opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second fight at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who worked behind a tight guard to narrowly win the more effective periods.
The spectators' acceptance decreased because of frequent holding, with Parker going down various instances during close exchanges.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, former world champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Motivates Local Rivalry Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by split-decision in a terrific Manchester vs Manchester battle to secure the European light heavyweight belt.
The venue grew hushed for a profoundly moving memorial ahead of the contest as a bell ceremony tolled in memory of the city's native Hatton, who succumbed aged 46 in last month.
It was the first major televised boxing event in the city since Hatton's passing. As the last bell disappeared, the stillness gave way to a shout of "there's just one Ricky Hatton".
The action during the bout equaled the sentiment. The eventual winner was floored by a left hook flush on the jaw in the second round, getting up unsteadily 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 damaged quickly, noticeable damage appearing under his face as the duo landed hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the intensity rarely dropped over twelve rounds.
Arthur barely secured the result with official scores of 114-114, narrow lead and wider gap, but both fighters were determined and brave, all the qualities their hero the legend embodied.
