British light-heavyweight Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a competitive 10-round fight at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a match where the techniques never quite clicked, with frequent clinching spoiling the fight.
The officials had it 96-94 to the winner, with the final judge a even score.
"It wasn't my greatest showing but how do champions respond? They succeed," Buatsi said in the arena as he was faced boos from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, deserved the win but the British boxer endured the second defeat of his 28-fight professional journey.
The Champion Claims Victory in Dull Match
The fighter's advancement has plateaued in recent times through contract problems and long spells of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to realize his potential - maybe in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter ready to take risks in a cagey initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to edge the better rounds.
The audience's tolerance diminished because of regular grabbing, with the challenger slipping to the canvas several times during clinches.
Parker closed well, but several stanzas were hard to judge. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of power puncher Benavidez, and Russian star Bivol leading the category, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Homage Fuels All-Manchester Contest
In the secondary fight, Arthur defeated Rea by divided decision in a terrific local rivalry battle to capture the continental belt.
The arena fell silent for a extremely emotional tribute ahead of the contest as ten bells tolled in honor of Manchester's own Hatton, who passed away aged 46 in September.
It was the first major televised boxing event in the urban center since Hatton's death. As the concluding sound ended, the quiet became a chant of "there's only one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was knocked down by a significant blow flush on the chin in the early round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red attire of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was marked up quickly, significant bruising forming under his orbital area as the fighters landed powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over 12 rounds.
The victor barely secured the decision with official scores of even score, close margin and clearer margin, but each competitor were relentless and full of heart, exactly what their inspiration Hatton represented.
