British light-heavyweight Buatsi earned a win yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a competitive 10-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective single shots in a match where the techniques failed to mesh, with constant grabbing marring the contest.
The scoring judges had it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my finest showing but what do champions do? They win," Buatsi commented in the ring as he was greeted with negative reactions from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts felt Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second setback of his 28-fight career.
Buatsi Secures Win in Uneventful Encounter
Buatsi's progress has plateaued in recent times through management issues and long spells of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under recent support.
He began cautiously, with both competitors prepared to take risks in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to edge the more effective rounds.
The spectators' acceptance decreased because of constant clinching, with the challenger slipping to the canvas multiple occasions during grappling.
The underdog ended stronger, but several stanzas were challenging to assess. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Homage Motivates Local Rivalry Battle
In the supporting bout, Arthur beat Rea by close verdict in a terrific local rivalry fight to capture the European light heavyweight belt.
The venue fell silent for a deeply poignant tribute prior to the bout as ten bells rang in remembrance of the city's native Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised fight night in the urban center since Hatton's passing. As the concluding sound ended, the silence became a chant of "there's just one Hatton".
The competition within the ring matched the feeling. The eventual winner was sent to the canvas by a left hook squarely on the face in the early round, getting up unsteadily to his footing on the referee's count.
But the red-colored attire of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up soon, heavy swelling developing under his face as the pair traded punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity rarely dropped over 12 rounds.
Arthur edged the decision with official scores of draw, narrow lead and 115-112, but each competitor were relentless and full of heart, all the qualities their hero Hatton stood for.
