UK light heavyweight Buatsi secured a victory yet disappointing debut to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a close ten-round bout at the Co-op Live Arena.
But the challenger found success, landing some telling individual punches in a fight where the styles never quite clicked, with excessive holding disrupting the contest.
The scoring judges judged it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest showing but what do champions do? They win," Buatsi said in the ringside as he was greeted with negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter suffered the second setback of his 28-match professional journey.
The Champion Earns Win in Uneventful Encounter
Buatsi's progress has stalled in recent years through contract problems and extended periods of lack of fights.
Earlier forecast as the next star of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers ready to take risks 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 in the contest, was competing in only his second bout at light-heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who worked behind a protective stance to narrowly win the cleaner stanzas.
The spectators' acceptance decreased amid constant clinching, with the challenger falling to the floor several times during close exchanges.
The underdog finished the stronger, but many rounds were difficult to score. Although, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi progresses, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Hatton Homage Fuels Manchester Derby Fight
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a excellent all-Manchester contest to capture the continental championship.
The venue grew hushed for a profoundly moving homage prior to the bout as ten bells rang in memory of the city's native Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the last bell faded, the silence gave way to a roar of "there's just one Hatton".
The action during the bout equaled the emotion. The eventual winner was floored by a significant blow directly to the jaw in the initial stage, getting up unsteadily to his feet on the eight count.
But the red-colored attire of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was damaged soon, noticeable damage forming under his face as the duo traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the action seldom decreased over the full distance.
Arthur edged the verdict with judges scorecards of even score, 115-113 and wider gap, but each competitor were relentless and courageous, everything their inspiration the legend stood for.
