British light heavyweight Buatsi secured a victory yet unimpressive debut to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But Parker landed significant shots, delivering effective clean blows in a match where the techniques didn't complement each other, with constant grabbing spoiling the fight.
Two judges judged it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my best display but how do champions respond? They win," Buatsi commented in the ring as he was faced boos from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Various analysts felt the challenger, 31, should have been awarded the win but the contender endured the second defeat of his 28-fight career.
The Champion Earns Win in Slow Encounter
Buatsi's progress has stalled in recent times through contract problems and long spells of lack of fights.
Once tipped as the rising talent of British boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with neither fighter prepared to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a tight guard to barely take the more effective rounds.
The crowd's patience diminished because of regular grabbing, with Parker slipping to the canvas multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Although, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
The victor progresses, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Hatton Memorial Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur beat Rea by close verdict in a terrific local rivalry battle to win the European light heavyweight title.
The stadium grew hushed for a deeply poignant homage before the fight as 10 bells rang in remembrance of local hero Hatton, who died aged 46 in last month.
It was the premier televised boxing event in the location since Hatton's passing. As the last bell disappeared, the quiet gave way to a roar of "there's only one Ricky Hatton".
The action during the bout matched the sentiment. The eventual winner was floored by a left hook flush on the face in the initial stage, getting up unsteadily to his footing on the eight count.
But the traditional red attire of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was damaged soon, noticeable damage appearing under his orbital area as the fighters exchanged punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the intensity rarely dropped over twelve rounds.
Arthur barely secured the verdict with scoring tallies of 114-114, 115-113 and 115-112, but the two athletes were determined and brave, all the qualities their idol the legend stood for.
