British light heavyweight Buatsi secured a victory yet disappointing start to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close ten-round contest at the Manchester venue.
But the challenger found success, connecting with powerful individual punches in a fight where the styles failed to mesh, with constant grabbing disrupting the contest.
The scoring judges judged it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest display but what defines champions? They succeed," Buatsi stated in the arena as he was met by negative reactions from the crowd.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Some ringside observers felt the challenger, 31, should have been awarded the win but the Derbyshire fighter suffered the second defeat of his 28-bout professional journey.
The Champion Earns Win in Slow Affair
His career development has slowed in the past few years through management issues and long spells of lack of fights.
Previously predicted as the future of the British fight scene, he now stands trying to fulfil that early promise - possibly in what seems like a last chance - under new promotional backing.
He opened tentatively, with the two boxers willing to take risks in a calculated opening few rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was making just his second fight at the higher weight class.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to narrowly win the more effective rounds.
The spectators' acceptance decreased during frequent holding, with Parker slipping to the canvas several times during grappling.
Parker ended stronger, but several stanzas were hard to judge. However, ex-champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Inspires Local Rivalry Battle
In the co-main event, Arthur overcame Rea by split-decision in a excellent all-Manchester fight to win the European light-heavyweight belt.
The stadium grew hushed for a deeply poignant memorial prior to the bout as a bell ceremony tolled in remembrance of the city's native Ricky Hatton, who passed away at age 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 gave way to a chant of "there's only one Ricky Hatton".
The action inside the ropes equaled the sentiment. Arthur was sent to the canvas by a powerful punch squarely on the face in the initial stage, rising shakily to his footing on the eight count.
But the red-colored attire of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was marked up early, significant bruising forming under his eye as the duo exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the intensity rarely dropped over twelve rounds.
The victor edged the result with scoring tallies of even score, narrow lead and 115-112, but the two athletes were persistent and full of heart, all the qualities their hero Hatton stood for.
