British light heavyweight Buatsi earned a win yet underwhelming beginning to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But the challenger found success, delivering effective single shots in a match where the techniques failed to mesh, with constant grabbing spoiling the contest.
Two judges scored it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best display but what defines champions? They prevail," Buatsi stated in the ringside as he was greeted with boos from the audience.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Several boxing experts felt Parker, thirty-one, deserved the decision but the British boxer endured the second loss of his 28-fight professional journey.
Buatsi Secures Win in Slow Affair
Buatsi's progress has slowed in recent years through management issues and extended periods of lack of fights.
Previously predicted as the next star of British boxing, he now is positioned trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter willing to take risks in a tentative initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second bout at light-heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to barely take the cleaner rounds.
The crowd's patience decreased amid frequent holding, with Parker slipping to the canvas several times during close exchanges.
The underdog ended stronger, but many rounds were hard to judge. Nevertheless, former world champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor progresses, but with the likes of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Tribute Fuels Manchester Derby Fight
In the secondary fight, Arthur overcame Rea by split-decision in a excellent all-Manchester contest to win the European light-heavyweight title.
The stadium became quiet for a extremely emotional homage ahead of the contest as 10 bells rang in remembrance of local hero Ricky Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast match card in the city since Hatton's passing. As the concluding sound faded, the silence became a chant of "there's just one Ricky Hatton".
The action during the bout reflected the emotion. The eventual winner was knocked down by a powerful punch flush on the face in the second round, rising shakily to his position on the count of eight.
But the red-colored equipment of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was damaged quickly, noticeable damage forming under his orbital area as the duo traded hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the pace seldom decreased over 12 rounds.
Arthur narrowly won the result with official scores of 114-114, narrow lead and 115-112, but each competitor were relentless and courageous, everything their inspiration Hatton represented.
