British light heavyweight Buatsi secured a victory yet disappointing beginning to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a close 10-round bout at the boxing arena.
But Parker found success, connecting with powerful clean blows in a contest where the approaches didn't complement each other, with frequent clinching disrupting the action.
The officials had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but what do champions do? They succeed," the victor stated in the ring as he was greeted with negative reactions from the spectators.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to claim a 20th pro success.
Various analysts felt Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
The Champion Secures Victory in Slow Encounter
Buatsi's progress has slowed in recent years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the future of the British fight scene, he now is positioned trying to realize his potential - possibly in what appears to be a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers willing to overcommit in a cagey initial rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was participating in his second fight at the higher weight class.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who operated with a solid defense to narrowly win the cleaner rounds.
The crowd's patience wore thin amid frequent holding, with the challenger going down several times during close exchanges.
Parker closed well, but multiple periods were challenging to assess. Nevertheless, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi progresses, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Inspires Manchester Derby Battle
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a excellent local rivalry contest to secure the European light-heavyweight championship.
The arena fell silent for a profoundly moving homage before the fight as 10 bells sounded in memory of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the final chime ended, the quiet gave way to a chant of "there's only one Hatton".
The competition during the bout equaled the feeling. Arthur was sent to the canvas by a significant blow directly to the jaw in the second round, standing uncertainly to his footing on the referee's count.
But the red-colored attire of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged soon, noticeable damage developing under his face as the fighters landed hard punches.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the intensity seldom decreased over the full distance.
Arthur narrowly won the verdict with judges scorecards of draw, narrow lead and 115-112, but each competitor were persistent and courageous, everything their idol the legend embodied.
