UK light heavyweight Buatsi made a winning yet underwhelming beginning to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a close 10-round fight at the Manchester venue.
But the challenger found success, landing some telling individual punches in a fight where the techniques didn't complement each other, with excessive holding disrupting the contest.
The officials scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi commented in the ring as he was met by disapproval from the crowd.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to secure a 20th pro success.
Several boxing experts felt Parker, thirty-one, should have been awarded the victory but the contender experienced the second loss of his 28-fight professional journey.
Buatsi Earns Triumph in Slow Affair
Buatsi's progress has stalled in recent years through management issues and considerable time of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to achieve expectations - possibly in what feels like a ultimate opportunity - under recent support.
He started carefully, with both competitors willing to be aggressive in a cagey initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second fight at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who operated with a tight guard to narrowly win the better periods.
The crowd's patience diminished during frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog closed well, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the presence of heavy hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Hatton Tribute Fuels Manchester Derby Contest
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a terrific all-Manchester contest to win the European light heavyweight title.
The arena grew hushed for a extremely emotional homage before the fight as a bell ceremony rang in honor of local hero Ricky Hatton, who passed away at age 46 in recently.
It was the premier televised fight night in the location since Hatton's passing. As the concluding sound faded, the quiet became a chant of "there's just one Ricky Hatton".
The competition during the bout equaled the emotion. Arthur was knocked down by a powerful punch directly to the jaw in the early round, getting up unsteadily to his position on the eight count.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, Rea - in competitive blue - was damaged early, noticeable damage appearing under his face as the pair exchanged punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the action hardly diminished over the full distance.
The victor barely secured the result with official scores of draw, close margin and wider gap, but both fighters were relentless and brave, exactly what their inspiration the legend embodied.
