British light-heavyweight Buatsi secured a victory yet unimpressive beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling single shots in a contest where the approaches didn't complement each other, with frequent clinching disrupting the action.
The scoring judges judged it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but what defines champions? They win," Buatsi said in the ring as he was met by negative reactions from the spectators.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Various analysts felt the challenger, thirty-one, merited the win but the contender endured the second defeat of his 28-bout career.
Buatsi Earns Win in Dull Match
The fighter's advancement has stalled in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter willing to be aggressive in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was competing in only his second appearance at light-heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who worked behind a tight guard to edge the cleaner rounds.
The crowd's patience decreased amid constant clinching, with Parker going down various instances during clinches.
Parker ended stronger, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor progresses, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Homage Inspires All-Manchester Battle
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a terrific all-Manchester contest to win the continental championship.
The arena fell silent for a deeply poignant homage prior to the bout as ten bells tolled in honor of Manchester's own Ricky Hatton, who died 46 years old in recently.
It was the premier televised fight night in the city since Hatton's passing. As the concluding sound faded, the silence became a shout of "there's only one Ricky Hatton".
The competition within the ring matched the feeling. Arthur was floored by a powerful punch directly to the jaw in the initial stage, rising shakily to his position on the referee's count.
But the red-colored equipment of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was injured quickly, noticeable damage forming under his eye as the fighters exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace hardly diminished over 12 rounds.
Arthur edged the verdict with scoring tallies of even score, close margin and wider gap, but the two athletes were persistent and courageous, everything their hero Hatton embodied.
