UK light heavyweight Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a competitive 10-round fight at the Manchester venue.
But the challenger had his moments, delivering effective clean blows in a fight where the styles didn't complement each other, with constant grabbing marring the contest.
The scoring judges scored it 96-94 for to the winner, with the third a even score.
"It wasn't my best performance but what defines champions? They prevail," the victor stated in the ring as he was faced negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second loss of his 28-bout professional journey.
The Champion Earns Win in Uneventful Match
The fighter's advancement has slowed in recent times through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who operated with a tight guard to barely take the cleaner rounds.
The spectators' acceptance wore thin amid constant clinching, with the challenger going down several times during grappling.
Parker finished the stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Hatton Tribute Motivates Local Rivalry Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to win the European light heavyweight title.
The arena fell silent for a profoundly moving memorial ahead of the contest as a bell ceremony sounded in memory of the city's native Ricky Hatton, who passed away 46 years old in last month.
It was the premier televised match card in the city since Hatton's death. As the concluding sound ended, the stillness gave way to a shout of "only one Ricky Hatton".
The action during the bout equaled the feeling. Arthur was floored by a left hook directly to the chin in the initial stage, standing uncertainly to his feet on the count of eight.
But the red-colored attire of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was injured soon, heavy swelling forming under his orbital area as the pair traded punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur barely secured the result with official scores of draw, 115-113 and clearer margin, but the two athletes were relentless and courageous, all the qualities their idol the legend embodied.
