British light heavyweight Buatsi earned a win yet disappointing beginning to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a competitive ten-round bout at the boxing arena.
But the challenger found success, delivering effective clean blows in a contest where the styles didn't complement each other, with frequent clinching spoiling the action.
Two judges had it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my best performance but how do champions respond? They win," the victor commented in the ringside as he was greeted with negative reactions from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th career victory.
Several boxing experts felt the challenger, thirty-one, merited the win but the British boxer endured the second defeat of his 28-bout career.
Buatsi Earns Victory in Dull Encounter
His career development has slowed in recent years through management issues and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to realize his potential - maybe in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors prepared to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who utilized a protective stance to barely take the more effective stanzas.
The spectators' acceptance decreased because of constant clinching, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog ended stronger, but several stanzas were hard to judge. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just a single round.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Memorial Motivates Local Rivalry Fight
In the supporting bout, Arthur overcame Rea by divided decision in a outstanding Manchester vs Manchester battle to win the European light-heavyweight belt.
The arena became quiet for a profoundly moving memorial before the fight as 10 bells rang in honor of Manchester's own Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the concluding sound disappeared, the stillness transitioned to a shout of "there's just one Ricky Hatton".
The action within the ring reflected the emotion. The eventual winner was knocked down by a significant blow directly to the chin in the initial stage, getting up unsteadily to his position on the count of eight.
But the traditional red equipment of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was injured quickly, significant bruising developing under his eye as the duo exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action hardly diminished over twelve rounds.
The victor narrowly won the decision with judges scorecards of draw, close margin and wider gap, but both fighters were relentless and full of heart, exactly what their hero Hatton represented.
