UK light-heavyweight Buatsi secured a victory yet unimpressive start to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a competitive ten-round bout at the Manchester venue.
But the challenger found success, connecting with powerful clean blows in a contest where the techniques failed to mesh, with excessive holding disrupting the contest.
Two judges judged it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," the victor commented in the arena as he was faced disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, should have been awarded the victory but the contender endured the second defeat of his 28-fight career.
The Champion Secures Triumph in Dull Match
Buatsi's progress has slowed in the past few years through promotional disputes and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to realize his potential - possibly in what feels like a last chance - under new promotional backing.
He opened tentatively, with both competitors ready to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was competing in only his second appearance at light heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who operated with a protective stance to edge the better periods.
The crowd's patience diminished during constant clinching, with the challenger slipping to the canvas multiple occasions during close exchanges.
The underdog closed well, but several stanzas were challenging to assess. Although, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Russian champion Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Fight
In the supporting bout, Arthur beat Rea by divided decision in a terrific all-Manchester battle to secure the continental championship.
The arena became quiet for a deeply poignant memorial prior to the bout as a bell ceremony tolled in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised fight night in the city since the passing of Hatton. As the last bell disappeared, the stillness transitioned to a chant of "there's only one Hatton".
The fighting during the bout matched the feeling. The eventual winner was knocked down by a powerful punch directly to the face in the initial stage, rising shakily to his position on the count of eight.
But the Manchester United-red shorts of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was damaged quickly, heavy swelling appearing under his face as the pair traded powerful shots.
The challenger, 27, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the action hardly diminished over the full distance.
The victor edged the decision with scoring tallies of even score, 115-113 and 115-112, but the two athletes were persistent and full of heart, exactly what their idol Hatton embodied.
