British light-heavyweight Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a split decision in a competitive ten-round contest at the boxing arena.
But Parker landed significant shots, delivering effective clean blows in a fight where the techniques didn't complement each other, with excessive holding marring the contest.
The scoring judges had it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They win," Buatsi commented in the arena as he was met by boos from the crowd.
The Londoner got back to winning after his first professional defeat - an memorable fight with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, deserved the decision but the contender experienced the second defeat of his 28-bout professional journey.
Buatsi Claims Victory in Uneventful Encounter
His career development has slowed in the past few years through management issues and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now finds himself trying to realize his potential - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers ready to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to edge the better rounds.
The audience's tolerance decreased during regular grabbing, with Parker going down several times during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
The victor progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Memorial Motivates Manchester Derby Contest
In the co-main event, Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester contest to capture the European light heavyweight belt.
The venue became quiet for a profoundly moving homage before the fight as ten bells rang in memory of local hero Hatton, who passed away 46 years old in recently.
It was the premier televised boxing event in the location since Hatton's passing. As the final chime faded, the stillness transitioned to a shout of "only one Ricky Hatton".
The fighting during the bout reflected the emotion. The eventual winner was sent to the canvas by a left hook squarely on the chin in the initial stage, standing uncertainly to his feet on the eight count.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was injured quickly, noticeable damage appearing under his face as the fighters exchanged powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the pace rarely dropped over the full distance.
Arthur edged the decision with official scores of 114-114, 115-113 and wider gap, but the two athletes were determined and full of heart, everything their hero the legend represented.
