UK light-heavyweight Buatsi made a winning yet disappointing debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a majority decision in a close ten-round contest at the boxing arena.
But Parker had his moments, landing some telling single shots in a fight where the techniques failed to mesh, with frequent clinching disrupting the action.
The officials scored it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but what defines champions? They succeed," the victor commented in the arena as he was met by disapproval from the spectators.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to secure a 20th pro success.
Various analysts thought the challenger, thirty-one, should have been awarded the win but the Derbyshire fighter endured the second setback of his 28-bout career.
Buatsi Claims Triumph in Dull Encounter
Buatsi's progress has plateaued in recent years through promotional disputes and extended periods of lack of fights.
Once tipped as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under fresh management.
He started carefully, with both competitors ready to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was making just his second fight at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for the favorite, who operated with a protective stance to edge the more effective stanzas.
The audience's tolerance diminished during constant clinching, with Parker falling to the floor several times during close exchanges.
The underdog finished the stronger, but several stanzas were hard to judge. However, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur defeated Rea by divided decision in a outstanding all-Manchester fight to win the European light-heavyweight belt.
The stadium grew hushed for a deeply poignant memorial before the fight as 10 bells sounded in memory of Manchester's own Ricky Hatton, who passed away at age 46 in September.
It was the premier televised match card in the location since Hatton's death. As the concluding sound disappeared, the quiet transitioned to a chant of "there's only one Hatton".
The competition during the bout reflected the sentiment. Arthur was floored by a left hook directly to the jaw in the early round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red attire of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was injured soon, noticeable damage forming under his eye as the duo traded punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the pace hardly diminished over twelve rounds.
The victor edged the verdict with official scores of even score, 115-113 and clearer margin, but the two athletes were determined and brave, exactly what their idol the legend represented.
