British light-heavyweight Buatsi earned a win yet unimpressive beginning to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But Parker found success, landing some telling clean blows in a fight where the techniques didn't complement each other, with frequent clinching spoiling the contest.
The scoring judges had it 96-94 to the winner, with the third a even score.
"It wasn't my greatest performance but what do champions do? They prevail," the victor stated in the ring as he was met by boos from the crowd.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts thought the challenger, 31, deserved the victory but the contender endured the second defeat of his 28-match career.
The Champion Earns Victory in Dull Match
The fighter's advancement has slowed in the past few years through management issues and considerable time of inactivity.
Previously predicted as the next star of British boxing, he now stands trying to realize his potential - maybe in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter willing to overcommit in a calculated opening few rounds.
Parker, whose only previous defeat came at the lower weight class 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 stayed in contention, making life awkward for the favorite, who utilized a tight guard to narrowly win the cleaner periods.
The crowd's patience diminished during regular grabbing, with the challenger slipping to the canvas several times during clinches.
The underdog closed well, but multiple periods were challenging to assess. Nevertheless, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Hatton Homage Fuels All-Manchester Battle
In the co-main event, Arthur beat Bradley Rea by divided decision in a excellent local rivalry fight to capture the European light-heavyweight championship.
The venue fell silent for a profoundly moving homage prior to the bout as 10 bells sounded in remembrance of local hero Hatton, who died aged 46 in September.
It was the initial significant broadcast fight night in the city since Hatton's death. As the concluding sound disappeared, the quiet transitioned to a roar of "there's just one Ricky Hatton".
The competition inside the ropes reflected the emotion. The eventual winner was knocked down by a significant blow directly to the chin in the second round, rising shakily to his feet on the count of eight.
But the traditional red shorts of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was injured quickly, heavy swelling appearing under his eye as the pair traded hard punches.
Rea, 27, landed power punches but Arthur, 34, responded in kind with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur barely secured the decision with official scores of even score, narrow lead and clearer margin, but both fighters were persistent and full of heart, exactly what their inspiration Hatton represented.
