UK light-heavyweight Buatsi earned a win yet underwhelming start to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a tight ten-round fight at the Manchester venue.
But the challenger found success, landing some telling single shots in a match where the styles didn't complement each other, with excessive holding spoiling the contest.
Two judges had it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my greatest showing but what defines champions? They prevail," the victor commented in the ringside as he was met by disapproval from the spectators.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought the challenger, 31, deserved the win but the British boxer endured the second setback of his 28-bout professional journey.
The Champion Claims Triumph in Dull Encounter
The fighter's advancement has plateaued in recent times through contract problems and extended periods of lack of fights.
Previously predicted as the rising talent of British boxing, he now stands trying to realize his potential - maybe in what appears to be a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter willing to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second bout at the higher weight class.
By the middle rounds, Parker had made it competitive, causing problems for the favorite, who utilized a protective stance to barely take the more effective stanzas.
The crowd's patience decreased during frequent holding, with the challenger going down several times during close exchanges.
Parker finished the stronger, but many rounds were hard to judge. Although, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Memorial Motivates All-Manchester Contest
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a excellent Manchester vs Manchester fight to win the European light-heavyweight championship.
The stadium grew hushed for a deeply poignant memorial prior to the bout as ten bells sounded in memory of the city's native Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the concluding sound faded, the stillness gave way to a chant of "only one Hatton".
The action within the ring matched the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the jaw in the early round, getting up unsteadily to his footing on the count of eight.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, Rea - in opposing blue - was damaged quickly, significant bruising appearing under his eye as the duo exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the intensity rarely dropped over the full distance.
The victor edged the verdict with scoring tallies of 114-114, narrow lead and clearer margin, but both fighters were relentless and full of heart, all the qualities their idol the legend represented.
