UK light heavyweight Buatsi secured a victory yet disappointing debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a tight 10-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful single shots in a contest where the techniques didn't complement each other, with excessive holding disrupting the action.
Two judges judged it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my finest display but what defines champions? They win," Buatsi commented in the ringside as he was greeted with disapproval from the audience.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts felt Parker, 31, deserved the win but the contender endured the second defeat of his 28-fight professional journey.
The Champion Claims Win in Uneventful Encounter
His career development has plateaued in recent years through contract problems and long spells of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to realize his potential - possibly in what feels like a final roll of the dice - under fresh management.
He started carefully, with both competitors ready to be aggressive in a cagey initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand mid-fight, was competing in only his second appearance at light heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for the favorite, who utilized a solid defense to narrowly win the cleaner rounds.
The crowd's patience decreased during constant clinching, with Parker slipping to the canvas several times during grappling.
Parker ended stronger, but many rounds were challenging to assess. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Hatton Memorial Inspires All-Manchester Contest
In the co-main event, Arthur defeated Bradley Rea by divided decision in a excellent Manchester vs Manchester contest to secure the European light heavyweight title.
The stadium grew hushed for a profoundly moving memorial before the fight as 10 bells tolled in honor of Manchester's own Hatton, who succumbed 46 years old in recently.
It was the first major televised fight night in the location since Hatton's death. As the last bell ended, the silence transitioned to a roar of "there's only one Hatton".
The action inside the ropes equaled the feeling. The eventual winner was knocked down by a left hook flush on the chin in the early round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red shorts of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was injured quickly, heavy swelling developing under his eye as the fighters exchanged hard punches.
The challenger, 27, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over twelve rounds.
The victor narrowly won the result with judges scorecards of draw, close margin and clearer margin, but both fighters were relentless and courageous, exactly what their idol Hatton embodied.
