British light heavyweight Buatsi secured a victory yet underwhelming debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive 10-round fight at the boxing arena.
But Parker landed significant shots, landing some telling single shots in a fight where the techniques failed to mesh, with excessive holding spoiling the action.
Two judges scored it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my best performance but what do champions do? They succeed," the victor said in the ring as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts felt Parker, thirty-one, deserved the victory but the British boxer endured the second defeat of his 28-bout career.
Buatsi Secures Triumph in Uneventful Affair
Buatsi's progress has plateaued in the past few years through contract problems and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a last chance - under fresh management.
He began cautiously, with neither fighter willing to take risks in a calculated 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 participating in his second appearance at light-heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to barely take the more effective periods.
The crowd's patience decreased during regular grabbing, with the challenger slipping to the canvas various instances during close exchanges.
The underdog ended stronger, but many rounds were hard to judge. Although, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the presence of power puncher Benavidez, and Russian champion Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Hatton Homage Fuels Manchester Derby Contest
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a terrific all-Manchester battle to capture the continental belt.
The venue became quiet for a extremely emotional homage before the fight as ten bells tolled in honor of the city's native Ricky Hatton, who passed away aged 46 in September.
It was the premier televised match card in the location since Hatton's passing. As the concluding sound faded, the stillness became a shout of "only one Ricky Hatton".
The action during the bout reflected the feeling. The eventual winner was floored by a left hook squarely on the face in the second round, getting up unsteadily to his feet on the referee's count.
But the red-colored shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was damaged early, heavy swelling developing under his eye as the duo traded hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor edged the decision with official scores of draw, close margin and 115-112, but the two athletes were relentless and brave, exactly what their idol the legend represented.
