UK light-heavyweight Buatsi made a winning yet underwhelming start to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a tight ten-round contest at the boxing arena.
But the challenger landed significant shots, landing some telling clean blows in a fight where the techniques failed to mesh, with frequent clinching marring the fight.
The officials judged it 96-94 for to the winner, with the third a 95-95.
"It wasn't my greatest performance but how do champions respond? They succeed," Buatsi said in the ringside as he was faced boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts felt the challenger, thirty-one, merited the decision but the contender endured the second setback of his 28-match career.
The Champion Secures Win in Dull Encounter
His career development has slowed in the past few years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to realize his potential - perhaps in what seems like a last chance - under recent support.
He opened tentatively, with neither fighter ready to take risks in a calculated initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second appearance at light heavyweight.
By the middle rounds, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to narrowly win the better periods.
The audience's tolerance decreased amid constant clinching, with Parker going down multiple occasions during clinches.
The underdog closed well, but multiple periods were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just one round.
The victor progresses, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Homage Motivates Local Rivalry Fight
In the co-main event, Arthur overcame Rea by divided decision in a excellent all-Manchester contest to capture the European light-heavyweight title.
The venue became quiet for a deeply poignant tribute prior to the bout as a bell ceremony tolled in honor of local hero Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the concluding sound ended, the silence became a chant of "there's only one Ricky Hatton".
The action within the ring reflected the emotion. Arthur was floored by a left hook flush on the jaw in the second round, rising shakily to his feet on the referee's count.
But the red-colored shorts of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was injured soon, heavy swelling forming under his face as the fighters landed powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the action rarely dropped over twelve rounds.
The victor barely secured the result with official scores of even score, 115-113 and wider gap, but both fighters were relentless and courageous, all the qualities their idol the legend stood for.
