UK light-heavyweight Buatsi made a winning yet disappointing start to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But the challenger found success, delivering effective single shots in a contest where the styles failed to mesh, with excessive holding spoiling the fight.
The officials scored it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest showing but how do champions respond? They succeed," the victor commented in the ring as he was faced boos from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a twentieth professional win.
Various analysts thought Parker, thirty-one, merited the win but the Derbyshire fighter suffered the second loss of his 28-bout career.
The Champion Earns Victory in Uneventful Encounter
His career development has plateaued in the past few years through contract problems and considerable time of lack of fights.
Previously predicted as the future of UK boxing, he now stands trying to realize his potential - perhaps in what seems like a final roll of the dice - under fresh management.
He began cautiously, with neither fighter prepared to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second appearance at light-heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who operated with a tight guard to barely take the better periods.
The spectators' acceptance wore thin during constant clinching, with the challenger going down multiple occasions during clinches.
The underdog finished the stronger, but several stanzas were challenging to assess. However, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Inspires All-Manchester Battle
In the supporting bout, Arthur beat Bradley Rea by split-decision in a excellent Manchester vs Manchester battle to capture the European light heavyweight championship.
The arena grew hushed for a profoundly moving memorial before the fight as 10 bells sounded in remembrance of local hero Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the concluding sound faded, the silence became a roar of "there's just one Ricky Hatton".
The fighting inside the ropes equaled the feeling. The eventual winner was floored by a powerful punch directly to the jaw in the second round, rising shakily to his footing on the eight count.
But the Manchester United-red shorts of the fighter soon advanced again. On the opposite side, Rea - in rival City blue - was marked up quickly, significant bruising forming under his face as the duo traded punishing blows.
The challenger, twenty-seven, landed power punches but the champion, 34, fought fire with fire with effective uppercuts as the action rarely dropped over 12 rounds.
Arthur barely secured the result with judges scorecards of 114-114, 115-113 and 115-112, but both fighters were relentless and full of heart, exactly what their inspiration the legend stood for.
