UK light-heavyweight Buatsi earned a win yet unimpressive start to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a majority decision in a competitive 10-round contest at the Manchester venue.
But Parker landed significant shots, delivering effective single shots in a contest where the techniques failed to mesh, with frequent clinching spoiling the action.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They succeed," the victor commented in the arena as he was greeted with disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts thought Parker, thirty-one, deserved the victory but the British boxer experienced the second setback of his 28-fight career.
The Champion Secures Triumph in Uneventful Encounter
Buatsi's progress has slowed in the past few years through promotional disputes and considerable time of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors prepared to overcommit in a tentative opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was making just his second fight at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who utilized a protective stance to edge the more effective periods.
The spectators' acceptance wore thin because of constant clinching, with Parker going down multiple occasions during clinches.
Parker closed well, but many rounds were hard to judge. However, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian champion Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Memorial Motivates All-Manchester Battle
In the co-main event, Lyndon Arthur beat Bradley Rea by close verdict in a excellent Manchester vs Manchester contest to win the European light-heavyweight belt.
The venue became quiet for a profoundly moving tribute ahead of the contest as ten bells rang in remembrance of Manchester's own Ricky Hatton, who died at age 46 in September.
It was the first major televised fight night in the urban center since the passing of Hatton. As the final chime disappeared, the quiet gave way to a shout of "there's only one Ricky Hatton".
The competition during the bout reflected the feeling. Arthur was sent to the canvas by a significant blow directly to the chin in the early round, rising shakily to his feet on the eight count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was damaged quickly, heavy swelling appearing under his face as the pair traded hard punches.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the action rarely dropped over twelve rounds.
The victor narrowly won the result with judges scorecards of draw, narrow lead and clearer margin, but both fighters were determined and brave, exactly what their hero Hatton embodied.
