British light-heavyweight Buatsi secured a victory yet unimpressive beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a fight where the styles never quite clicked, with frequent clinching spoiling the action.
Two judges had it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest display but what do champions do? They win," Buatsi said in the ringside as he was faced negative reactions from the audience.
The Londoner got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts thought Parker, 31, deserved the win but the Derbyshire fighter endured the second setback of his 28-match career.
Buatsi Secures Triumph in Dull Affair
Buatsi's progress has plateaued in recent years through contract problems and long spells of inactivity.
Once tipped as the next star of British boxing, he now is positioned trying to realize his potential - perhaps in what seems like a final roll of the dice - under recent support.
He started carefully, with the two boxers ready to be aggressive in a tentative early stages.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to edge the more effective rounds.
The audience's tolerance wore thin because of constant clinching, with the challenger slipping to the canvas several times during grappling.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the presence of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Fuels All-Manchester Fight
In the co-main event, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry contest to capture the continental belt.
The venue grew hushed for a profoundly moving homage ahead of the contest as a bell ceremony rang in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in September.
It was the first major televised fight night in the location since Hatton's death. As the final chime faded, the stillness gave way to a shout of "only one Hatton".
The competition within the ring matched the sentiment. Arthur was floored by a powerful punch flush on the chin in the initial stage, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. On the opposite side, Rea - in opposing blue - was marked up soon, noticeable damage appearing under his eye as the pair landed hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over 12 rounds.
Arthur barely secured the decision with scoring tallies of draw, narrow lead and wider gap, but both fighters were relentless and courageous, exactly what their hero Hatton represented.
