British light-heavyweight Buatsi earned a win yet underwhelming start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round fight at the boxing arena.
But Parker had his moments, landing some telling single shots in a match where the styles didn't complement each other, with constant grabbing spoiling the fight.
The officials had it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They win," the victor said in the arena as he was faced negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts felt Parker, thirty-one, merited the decision but the Derbyshire fighter suffered the second defeat of his 28-bout professional journey.
The Champion Earns Victory in Slow Match
His career development has slowed in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the next star of British boxing, he now stands trying to realize his potential - possibly in what appears to be a last chance - under recent support.
He opened tentatively, with neither fighter prepared to be aggressive in a calculated opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a tight guard to edge the cleaner periods.
The spectators' acceptance wore thin because of constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
The underdog closed well, but several stanzas were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Homage Motivates All-Manchester Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific all-Manchester contest to secure the European light-heavyweight championship.
The stadium became quiet for a deeply poignant homage ahead of the contest as 10 bells sounded in remembrance of Manchester's own Hatton, who succumbed 46 years old in September.
It was the first major televised match card in the location since Hatton's death. As the last bell faded, the silence transitioned to a chant of "there's just one Ricky Hatton".
The competition inside the ropes matched the feeling. The eventual winner was knocked down by a left hook squarely on the face in the initial stage, getting up unsteadily to his footing on the referee's count.
But the red-colored attire of the fighter soon came forward again. On the opposite side, Rea - in rival City blue - was damaged quickly, noticeable damage forming under his orbital area as the fighters exchanged punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with effective uppercuts as the intensity hardly diminished over twelve rounds.
Arthur edged the verdict with judges scorecards of 114-114, close margin and wider gap, but each competitor were relentless and courageous, everything their idol Hatton embodied.
