British light heavyweight Buatsi made a winning yet disappointing debut to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close ten-round bout at the Manchester venue.
But the challenger found success, delivering effective individual punches in a contest where the styles didn't complement each other, with frequent clinching disrupting the action.
The officials had it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi stated in the ring as he was faced disapproval from the audience.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Several boxing experts felt the challenger, 31, deserved the decision but the British boxer endured the second loss of his 28-fight career.
Buatsi Secures Victory in Dull Affair
Buatsi's progress has slowed in the past few years through management issues and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now finds himself trying to realize his potential - maybe in what feels like a final roll of the dice - under fresh management.
He began cautiously, with both competitors prepared to take risks in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight 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 halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a tight guard to barely take the more effective stanzas.
The spectators' acceptance decreased because of constant clinching, with the challenger falling to the floor several times during grappling.
Parker ended stronger, but multiple periods were difficult to score. Although, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
The victor advances, but with the caliber of power puncher Benavidez, and Russian star Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Memorial Inspires All-Manchester Battle
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry battle to secure the European light-heavyweight belt.
The arena grew hushed for a deeply poignant homage before the fight as a bell ceremony rang in remembrance of Manchester's own Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the last bell ended, the stillness gave way to a chant of "there's only one Hatton".
The action within the ring equaled the feeling. The eventual winner was floored by a significant blow flush on the face in the initial stage, getting up unsteadily to his feet on the referee's count.
But the traditional red shorts of the fighter soon came forward again. On the opposite side, Rea - in opposing blue - was damaged early, heavy swelling forming under his orbital area as the pair exchanged hard punches.
Rea, 27, delivered effective strikes but the champion, 34, matched the intensity with powerful upward punches as the action seldom decreased over twelve rounds.
Arthur narrowly won the verdict with scoring tallies of draw, narrow lead and clearer margin, but both fighters were relentless and brave, exactly what their idol the legend embodied.
