UK light-heavyweight Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close 10-round bout at the Manchester venue.
But Parker landed significant shots, delivering effective single shots in a contest where the styles never quite clicked, with constant grabbing disrupting the contest.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my best performance but what do champions do? They win," Buatsi commented in the ring as he was met by boos from the spectators.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts thought Parker, thirty-one, deserved the decision but the contender suffered the second defeat of his 28-fight career.
The Champion Claims Victory in Slow Match
Buatsi's progress has slowed in recent years through management issues and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with both competitors willing to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second fight at the higher weight class.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who utilized a protective stance to barely take the cleaner rounds.
The spectators' acceptance decreased during regular grabbing, with Parker going down various instances during clinches.
The underdog closed well, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi advances, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Memorial Fuels Manchester Derby Battle
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a terrific local rivalry fight to secure the continental belt.
The arena became quiet for a deeply poignant memorial ahead of the contest as 10 bells tolled in honor of local hero Hatton, who passed away aged 46 in September.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the last bell faded, the stillness gave way to a roar of "there's only one Hatton".
The action within the ring equaled the feeling. Arthur was sent to the canvas by a significant blow directly to the jaw in the initial stage, standing uncertainly to his feet on the count of eight.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was marked up early, heavy swelling forming under his orbital area as the fighters traded hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over the full distance.
The victor edged the decision with judges scorecards of draw, 115-113 and wider gap, but each competitor were determined and courageous, everything their idol the legend embodied.
