British light-heavyweight Buatsi made a winning yet unimpressive start to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling individual punches in a contest where the styles failed to mesh, with excessive holding marring the action.
The officials scored it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They prevail," the victor stated in the ringside as he was greeted with disapproval from the crowd.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers felt the challenger, thirty-one, deserved the win but the British boxer endured the second loss of his 28-fight professional journey.
The Champion Claims Triumph in Dull Match
Buatsi's progress has stalled in recent times through contract problems and long spells of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to realize his potential - perhaps in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers ready to be aggressive in a tentative opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who operated with a tight guard to edge the more effective periods.
The audience's tolerance diminished amid regular grabbing, with Parker falling to the floor multiple occasions during clinches.
Parker closed well, but multiple periods were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the likes of hard hitter Benavidez, and Russian star Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Motivates All-Manchester Battle
In the secondary fight, Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester contest to win the European light heavyweight title.
The venue grew hushed for a extremely emotional memorial ahead of the contest as ten bells tolled in honor of Manchester's own Hatton, who died 46 years old in September.
It was the first major televised boxing event in the city since Hatton's death. As the last bell ended, the quiet became a chant of "only one Hatton".
The action during the bout matched the feeling. Arthur was floored by a left hook squarely on the face in the initial stage, getting up unsteadily to his feet on the eight count.
But the red-colored attire of the fighter soon advanced again. On the opposite side, Rea - in rival City blue - was injured early, heavy swelling developing under his eye as the pair exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the action rarely dropped over 12 rounds.
Arthur edged the verdict with judges scorecards of 114-114, close margin and 115-112, but each competitor were determined and brave, everything their inspiration Hatton represented.
