British light heavyweight Buatsi made a winning yet disappointing start to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a tight ten-round fight at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a fight where the approaches didn't complement each other, with frequent clinching disrupting the fight.
The officials had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They succeed," Buatsi said in the ring as he was faced negative reactions from the spectators.
The Londoner got back to winning after his initial pro loss - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts thought the challenger, 31, merited the victory but the contender endured the second setback of his 28-match professional journey.
Buatsi Secures Victory in Dull Affair
The fighter's advancement has plateaued in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors prepared to take risks in a cagey early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in 2022 after breaking his hand during the bout, was making just his second bout at light heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to barely take the cleaner rounds.
The spectators' acceptance diminished amid regular grabbing, with Parker slipping to the canvas several times during grappling.
The underdog closed well, but several stanzas were difficult to score. However, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding local rivalry battle to capture the European light-heavyweight title.
The stadium became quiet for a deeply poignant tribute before the fight as 10 bells sounded in honor of the city's native Hatton, who succumbed aged 46 in last month.
It was the first major televised fight night in the urban center since Hatton's death. As the final chime disappeared, the silence transitioned to a chant of "there's just one Hatton".
The competition inside the ropes matched the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the jaw in the early round, rising shakily to his footing on the eight count.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, Rea - in rival City blue - was marked up soon, significant bruising developing under his orbital area as the pair exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the result with judges scorecards of draw, narrow lead and 115-112, but the two athletes were persistent and full of heart, exactly what their inspiration Hatton represented.
