UK light-heavyweight Buatsi made a winning yet disappointing start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a competitive 10-round fight at the boxing arena.
But Parker landed significant shots, landing some telling single shots in a match where the styles didn't complement each other, with constant grabbing marring the action.
The officials had it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They succeed," the victor commented in the ring as he was faced disapproval from the audience.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in February - to secure a 20th career victory.
Various analysts felt the challenger, thirty-one, should have been awarded the win but the Derbyshire fighter endured the second loss of his 28-match career.
The Champion Earns Victory in Uneventful Encounter
Buatsi's progress has stalled in recent years through management issues and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers willing to take risks in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second fight at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who utilized a protective stance to edge the more effective periods.
The audience's tolerance diminished during frequent holding, with the challenger going down various instances during close exchanges.
Parker finished the stronger, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor moves on, but with the likes of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Memorial Motivates All-Manchester Battle
In the supporting bout, Arthur beat Bradley Rea by close verdict in a excellent local rivalry fight to secure the European light heavyweight title.
The venue grew hushed for a deeply poignant homage before the fight as a bell ceremony sounded in memory of local hero Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the last bell ended, the silence became a roar of "only one Ricky Hatton".
The action within the ring equaled the emotion. Arthur was knocked down by a significant blow directly to the jaw in the second round, standing uncertainly to his feet on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was damaged soon, heavy swelling forming under his eye as the duo traded punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over 12 rounds.
Arthur edged the decision with scoring tallies of draw, narrow lead and wider gap, but the two athletes were persistent and courageous, all the qualities their inspiration the legend embodied.
