British light-heavyweight Buatsi secured a victory yet unimpressive beginning to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a close ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective clean blows in a contest where the approaches failed to mesh, with excessive holding marring the action.
The officials judged it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my greatest display but how do champions respond? They win," Buatsi stated in the ringside as he was met by disapproval from the audience.
The Londoner got back to winning after his initial pro loss - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Various analysts believed the challenger, thirty-one, merited the victory but the contender experienced the second setback of his 28-match career.
The Champion Claims Triumph in Slow Affair
The fighter's advancement has slowed in recent times through management issues and long spells of lack of fights.
Previously predicted as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with both competitors ready to be aggressive in a calculated early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second appearance at the higher weight class.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who utilized a protective stance to barely take the cleaner stanzas.
The spectators' acceptance diminished during frequent holding, with the challenger slipping to the canvas several times during close exchanges.
Parker ended stronger, but several stanzas were challenging to assess. Although, former world champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the likes of hard hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Motivates All-Manchester Contest
In the secondary fight, Arthur overcame Rea by close verdict in a excellent all-Manchester contest to secure the continental championship.
The stadium fell silent for a deeply poignant memorial before the fight as a bell ceremony rang in remembrance of local hero Ricky Hatton, who succumbed 46 years old in last month.
It was the premier televised match card in the location since Hatton's passing. As the last bell disappeared, the stillness became a roar of "there's just one Hatton".
The fighting inside the ropes equaled the emotion. Arthur was floored by a left hook flush on the chin in the early round, getting up unsteadily to his feet on the eight count.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was injured soon, noticeable damage developing under his orbital area as the pair traded punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the action hardly diminished over the full distance.
The victor edged the decision with judges scorecards of draw, 115-113 and wider gap, but each competitor were relentless and courageous, exactly what their idol the legend stood for.
