British light heavyweight Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But the challenger found success, connecting with powerful single shots in a contest where the techniques didn't complement each other, with excessive holding disrupting the fight.
Two judges judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but what do champions do? They win," Buatsi commented in the ring as he was met by disapproval from the audience.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, deserved the decision but the British boxer experienced the second loss of his 28-bout professional journey.
Buatsi Claims Victory in Slow Encounter
The fighter's advancement has plateaued in recent years through contract problems and long spells of lack of fights.
Previously predicted as the future of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what seems like a last chance - under new promotional backing.
He began cautiously, with both competitors willing to overcommit in a calculated opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was making just his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a tight guard to barely take the better periods.
The audience's tolerance diminished amid constant clinching, with the challenger going down several times during grappling.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Hatton Memorial Inspires Manchester Derby Fight
In the supporting bout, Arthur beat Rea by close verdict in a outstanding all-Manchester battle to win the European light heavyweight title.
The stadium became quiet for a extremely emotional homage before the fight as 10 bells rang in remembrance of the city's native Ricky Hatton, who died at age 46 in last month.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the concluding sound disappeared, the stillness transitioned to a chant of "only one Ricky Hatton".
The action inside the ropes equaled the sentiment. The eventual winner was knocked down by a powerful punch flush on the chin in the early round, rising shakily to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was injured early, noticeable damage developing under his eye as the duo traded powerful shots.
The challenger, 27, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the action seldom decreased over the full distance.
Arthur edged the verdict with judges scorecards of draw, 115-113 and wider gap, but the two athletes were persistent and brave, everything their inspiration Hatton embodied.
