British light-heavyweight Buatsi secured a victory yet unimpressive beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a competitive ten-round bout at the Manchester venue.
But Parker found success, landing some telling clean blows in a match where the styles never quite clicked, with excessive holding marring the contest.
The scoring judges scored it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best performance but how do champions respond? They prevail," the victor said in the ringside as he was greeted with boos from the crowd.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Some ringside observers thought the challenger, thirty-one, should have been awarded the win but the Derbyshire fighter suffered the second setback of his 28-fight career.
The Champion Claims Win in Dull Affair
Buatsi's progress has plateaued in recent times through contract problems and considerable time of lack of fights.
Once tipped as the next star of the British fight scene, he now finds himself trying to achieve expectations - maybe in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors ready to overcommit in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand in the contest, 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 utilized a protective stance to edge the cleaner rounds.
The crowd's patience wore thin during regular grabbing, with Parker slipping to the canvas several times during close exchanges.
The underdog finished the stronger, but multiple periods were difficult to score. However, previous titleholder Carl Frampton - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi advances, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Hatton Memorial Inspires Local Rivalry Contest
In the secondary fight, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent local rivalry fight to secure the European light heavyweight championship.
The arena fell silent for a profoundly moving memorial ahead of the contest as a bell ceremony tolled in honor of the city's native Ricky Hatton, who passed away aged 46 in recently.
It was the first major televised match card in the urban center since Hatton's death. As the concluding sound ended, the silence transitioned to a roar of "only one Hatton".
The competition within the ring matched the feeling. The eventual winner was knocked down by a left hook flush on the jaw in the initial stage, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was damaged quickly, heavy swelling appearing under his eye as the fighters exchanged powerful shots.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the action rarely dropped over 12 rounds.
The victor edged the result with judges scorecards of draw, 115-113 and clearer margin, but each competitor were persistent and brave, everything their idol the legend represented.
