British light heavyweight Buatsi earned a win yet disappointing beginning to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a close ten-round bout at the boxing arena.
But the challenger had his moments, landing some telling individual punches in a contest where the approaches never quite clicked, with frequent clinching disrupting the fight.
Two judges had it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest showing but how do champions respond? They prevail," Buatsi stated in the ringside as he was met by disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a 20th pro success.
Some ringside observers believed Parker, 31, merited the win but the contender suffered the second loss of his 28-match career.
The Champion Secures Victory in Dull Encounter
Buatsi's progress has stalled in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors ready to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second appearance at the higher weight class.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a tight guard to edge the cleaner periods.
The crowd's patience decreased during constant clinching, with Parker falling to the floor multiple occasions during clinches.
Parker finished the stronger, but many rounds were hard to judge. Nevertheless, ex-champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Hatton Homage Motivates All-Manchester Fight
In the co-main event, Lyndon Arthur defeated Bradley Rea by divided decision in a terrific all-Manchester battle to win the European light-heavyweight title.
The stadium grew hushed for a deeply poignant memorial ahead of the contest as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the concluding sound disappeared, the stillness transitioned to a shout of "only one Ricky Hatton".
The action inside the ropes equaled the sentiment. Arthur was floored by a left hook directly to the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored attire of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was injured early, significant bruising forming under his eye as the fighters exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the intensity seldom decreased over the full distance.
The victor narrowly won the result with official scores of 114-114, close margin and wider gap, but each competitor were relentless and full of heart, everything their idol Hatton stood for.
