British light-heavyweight Buatsi earned a win yet underwhelming beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close 10-round fight at the Manchester venue.
But the challenger found success, delivering effective individual punches in a match where the styles never quite clicked, with excessive holding spoiling the fight.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest performance but how do champions respond? They win," the victor commented in the ringside as he was faced boos from the audience.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to secure a 20th career victory.
Various analysts felt the challenger, 31, deserved the victory but the Derbyshire fighter endured the second setback of his 28-match career.
Buatsi Claims Triumph in Slow Affair
His career development has plateaued in recent years through contract problems and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to achieve expectations - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with the two boxers willing to take risks in a cagey initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who operated with a protective stance to barely take the better periods.
The crowd's patience decreased amid frequent holding, with Parker going down multiple occasions during close exchanges.
Parker closed well, but multiple periods were difficult to score. However, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just a single round.
Buatsi moves on, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a outstanding Manchester vs Manchester battle to secure the continental championship.
The arena fell silent for a extremely emotional memorial ahead of the contest as 10 bells rang in remembrance of the city's native Hatton, who passed away at age 46 in last month.
It was the first major televised boxing event in the city since the passing of Hatton. As the last bell ended, the stillness became a shout of "there's just one Ricky Hatton".
The competition within the ring matched the feeling. The eventual winner was knocked down by a left hook flush on the jaw in the early round, standing uncertainly to his footing on the count of eight.
But the red-colored attire of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was damaged quickly, heavy swelling developing under his eye as the fighters exchanged powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with powerful upward punches as the action rarely dropped over 12 rounds.
Arthur edged the result with scoring tallies of even score, close margin and wider gap, but the two athletes were relentless and brave, all the qualities their inspiration the legend stood for.
