British light-heavyweight Buatsi secured a victory yet underwhelming start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful single shots in a match where the techniques failed to mesh, with excessive holding spoiling the action.
The officials judged it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my finest showing but how do champions respond? They win," the victor commented in the ringside as he was greeted with boos from the spectators.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a 20th career victory.
Various analysts felt Parker, 31, merited the win but the Derbyshire fighter endured the second setback of his 28-match professional journey.
His career development has stalled in recent years through contract problems and extended periods of inactivity.
Once tipped as the next star of the British fight scene, he now finds himself trying to realize his potential - maybe in what appears to be a last chance - under recent support.
He began cautiously, with the two boxers ready to take risks in a tentative initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after damaging his hand in the contest, was participating in his second appearance at light heavyweight.
By the middle rounds, Parker had made it competitive, causing problems for the favorite, who operated with a tight guard to barely take the better periods.
The spectators' acceptance wore thin during regular grabbing, with the challenger going down multiple occasions during close exchanges.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry fight to win the continental title.
The arena became quiet for a deeply poignant homage ahead of the contest as ten bells tolled in memory of local hero Hatton, who died at age 46 in recently.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the concluding sound ended, the stillness became a roar of "only one Hatton".
The fighting inside the ropes reflected the sentiment. Arthur was sent to the canvas by a powerful punch flush on the face in the early round, rising shakily to his feet on the count of eight.
But the Manchester United-red shorts of the fighter soon advanced again. From the other corner, the opponent - in opposing blue - was marked up quickly, noticeable damage appearing under his eye as the pair exchanged punishing blows.
Rea, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor narrowly won the verdict with judges scorecards of draw, close margin and clearer margin, but both fighters were persistent and full of heart, all the qualities their idol Hatton embodied.
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