UK light-heavyweight Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive ten-round bout at the boxing arena.
But the challenger found success, delivering effective single shots in a match where the approaches never quite clicked, with excessive holding disrupting the fight.
The officials scored it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest display but what defines champions? They succeed," Buatsi commented in the ring as he was met by boos from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers felt the challenger, 31, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-match professional journey.
The Champion Claims Victory in Dull Encounter
His career development has slowed in the past few years through promotional disputes and long spells of lack of fights.
Once tipped as the next star of British boxing, he now stands trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter willing to be aggressive in a tentative opening few rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had stayed in contention, causing problems for the favorite, who worked behind a tight guard to edge the cleaner rounds.
The crowd's patience wore thin during constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
Parker closed well, but several stanzas were challenging to assess. Although, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific all-Manchester battle to secure the continental championship.
The arena became quiet for a extremely emotional tribute prior to the bout as a bell ceremony tolled in memory of local hero Hatton, who died 46 years old in last month.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the last bell disappeared, the quiet became a chant of "there's only one Hatton".
The fighting during the bout equaled the emotion. Arthur was floored by a left hook flush on the chin in the early round, standing uncertainly to his feet on the eight count.
But the traditional red shorts of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was marked up early, heavy swelling forming under his face as the duo traded powerful shots.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the intensity seldom decreased over twelve rounds.
Arthur narrowly won the verdict with scoring tallies of even score, narrow lead and clearer margin, but each competitor were determined and full of heart, everything their hero the legend represented.
