UK light heavyweight Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a competitive ten-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a match where the styles never quite clicked, with frequent clinching spoiling the action.
Two judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my finest display but what do champions do? They win," the victor commented in the arena as he was faced boos from the crowd.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Various analysts felt the challenger, thirty-one, should have been awarded the win but the Derbyshire fighter suffered the second loss of his 28-match career.
Buatsi Secures Victory in Dull Match
The fighter's advancement has plateaued in recent times through contract problems and long spells of lack of fights.
Earlier forecast as the future of the British fight scene, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter prepared to take risks in a calculated initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second bout at light heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who operated with a tight guard to barely take the more effective periods.
The crowd's patience decreased because of regular grabbing, with the challenger going down several times during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the co-main event, Arthur overcame Rea by split-decision in a excellent all-Manchester battle to capture the European light heavyweight title.
The arena became quiet for a deeply poignant homage before the fight as a bell ceremony rang in memory of the city's native Ricky Hatton, who succumbed aged 46 in last month.
It was the first major televised match card in the city since Hatton's passing. As the last bell disappeared, the stillness transitioned to a chant of "there's just one Hatton".
The competition inside the ropes reflected the emotion. The eventual winner was sent to the canvas by a left hook squarely on the chin in the second round, standing uncertainly to his footing on the count of eight.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was injured early, significant bruising developing under his orbital area as the duo landed hard punches.
Rea, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
Arthur barely secured the verdict with official scores of draw, close margin and clearer margin, but each competitor were determined and courageous, exactly what their inspiration Hatton embodied.
