British light heavyweight Buatsi earned a win yet underwhelming start to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a tight ten-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a match where the approaches didn't complement each other, with excessive holding disrupting the contest.
Two judges scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest performance but what defines champions? They win," the victor stated in the ringside as he was met by disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts felt the challenger, thirty-one, merited the decision but the British boxer endured the second setback of his 28-match professional journey.
The Champion Secures Victory in Slow Match
Buatsi's progress has slowed in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the next star of the British fight scene, he now is positioned trying to realize his potential - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with both competitors ready to be aggressive in a cagey early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second bout at the higher weight class.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to edge the more effective periods.
The audience's tolerance decreased amid regular grabbing, with Parker slipping to the canvas several times during grappling.
Parker finished the stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor advances, but with the likes of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Tribute Inspires Local Rivalry Contest
In the supporting bout, Arthur beat Bradley Rea by divided decision in a terrific local rivalry contest to capture the European light-heavyweight belt.
The venue grew hushed for a extremely emotional homage ahead of the contest as a bell ceremony rang in honor of the city's native Hatton, who died at age 46 in last month.
It was the premier televised boxing event in the location since Hatton's death. As the final chime ended, the stillness transitioned to a chant of "there's just one Hatton".
The fighting during the bout matched the emotion. The eventual winner was sent to the canvas by a left hook flush on the chin in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored attire of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was marked up soon, noticeable damage developing under his face as the duo traded punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace hardly diminished over 12 rounds.
Arthur narrowly won the verdict with scoring tallies of draw, close margin and clearer margin, but the two athletes were relentless and brave, exactly what their inspiration Hatton stood for.
