British light heavyweight Buatsi secured a victory yet underwhelming debut to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a tight ten-round fight at the boxing arena.
But the challenger had his moments, connecting with powerful single shots in a fight where the approaches didn't complement each other, with frequent clinching spoiling the action.
Two judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest display but what defines champions? They succeed," Buatsi commented in the arena as he was faced disapproval from the crowd.
The British fighter bounced back after his maiden career setback - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts felt Parker, thirty-one, merited the decision but the Derbyshire fighter endured the second loss of his 28-bout career.
Buatsi Earns Victory in Slow Match
His career development has stalled in recent years through management issues and long spells of lack of fights.
Previously predicted as the next star of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what seems like a last chance - under fresh management.
He opened tentatively, with the two boxers willing to take risks in a cagey early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a solid defense to edge the better stanzas.
The audience's tolerance decreased because of frequent holding, with the challenger going down several times during clinches.
The underdog closed well, but many rounds were hard to judge. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Memorial Fuels Local Rivalry Battle
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a outstanding local rivalry fight to secure the European light-heavyweight title.
The arena fell silent for a deeply poignant homage before the fight as a bell ceremony rang in remembrance of Manchester's own Hatton, who died at age 46 in September.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the last bell faded, the silence became a roar of "there's just one Hatton".
The action inside the ropes reflected the emotion. Arthur was knocked down by a powerful punch directly to the chin in the initial stage, rising shakily to his feet on the count of eight.
But the traditional red equipment of the fighter soon came forward again. From the other corner, the opponent - in competitive blue - was marked up soon, heavy swelling developing under his eye as the fighters traded hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace hardly diminished over twelve rounds.
Arthur barely secured the decision with scoring tallies of 114-114, narrow lead and 115-112, but the two athletes were determined and full of heart, all the qualities their idol Hatton embodied.
