British light heavyweight Buatsi made a winning yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a competitive 10-round fight at the Co-op Live Arena.
But Parker found success, landing some telling individual punches in a fight where the styles never quite clicked, with excessive holding disrupting the action.
Two judges scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my best showing but what defines champions? They win," Buatsi stated in the ringside as he was faced disapproval from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, should have been awarded the win but the Derbyshire fighter experienced the second loss of his 28-match professional journey.
The Champion Earns Win in Uneventful Match
His career development has slowed in recent times through management issues and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a final roll of the dice - under recent support.
He began cautiously, with both competitors willing to take risks in a calculated initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second bout at the higher weight class.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who worked behind a tight guard to edge the better rounds.
The spectators' acceptance diminished during regular grabbing, with Parker slipping to the canvas various instances during grappling.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Hatton Memorial Motivates Manchester Derby Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry contest to secure the continental belt.
The venue became quiet for a extremely emotional homage prior to the bout as ten bells rang in remembrance of Manchester's own Hatton, who passed away at age 46 in September.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime disappeared, the stillness transitioned to a shout of "there's only one Ricky Hatton".
The action during the bout reflected the emotion. The eventual winner was sent to the canvas by a significant blow directly to the jaw in the early round, standing uncertainly to his position on the eight count.
But the traditional red attire of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was injured quickly, noticeable damage forming under his eye as the duo landed hard punches.
Rea, 27, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over twelve rounds.
The victor edged the decision with scoring tallies of draw, narrow lead and wider gap, but the two athletes were persistent and brave, exactly what their hero Hatton stood for.
