British light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a competitive ten-round bout at the boxing arena.
But Parker found success, connecting with powerful single shots in a contest where the approaches failed to mesh, with frequent clinching marring the action.
The scoring judges judged it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my finest display but how do champions respond? They prevail," Buatsi said in the ring as he was faced negative reactions from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Several boxing experts believed the challenger, thirty-one, merited the decision but the contender endured the second setback of his 28-fight professional journey.
Buatsi Secures Triumph in Dull Match
Buatsi's progress has plateaued in recent times through management issues and long spells of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to realize his potential - maybe in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter ready to be aggressive in a cagey initial rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who operated with a solid defense to edge the more effective periods.
The audience's tolerance diminished during constant clinching, with the challenger falling to the floor various instances during grappling.
Parker closed well, but many rounds were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just a single round.
Buatsi progresses, but with the presence of hard hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Hatton Memorial Inspires Manchester Derby Contest
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to capture the continental belt.
The arena grew hushed for a deeply poignant homage ahead of the contest as ten bells sounded in remembrance of local hero Ricky Hatton, who succumbed 46 years old in last month.
It was the first major televised fight night in the location since the passing of Hatton. As the final chime faded, the quiet became a chant of "there's only one Ricky Hatton".
The action during the bout matched the emotion. Arthur was floored by a left hook directly to the face in the second round, standing uncertainly to his position on the referee's count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. From the other corner, Rea - in opposing blue - was damaged early, heavy swelling appearing under his orbital area as the duo landed punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the decision with official scores of even score, 115-113 and clearer margin, but each competitor were persistent and courageous, exactly what their idol the legend stood for.
