British light heavyweight Buatsi secured a victory yet disappointing start to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a contest where the approaches never quite clicked, with excessive holding spoiling the contest.
The officials had it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi stated in the ring as he was met by negative reactions from the crowd.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts believed the challenger, 31, merited the victory but the contender suffered the second loss of his 28-match career.
The Champion Earns Triumph in Slow Encounter
The fighter's advancement has slowed in recent times through management issues and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what seems like a last chance - under recent support.
He opened tentatively, with the two boxers prepared to be aggressive in a tentative early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second fight at the higher weight class.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who worked behind a tight guard to barely take the better periods.
The crowd's patience decreased amid regular grabbing, with Parker falling to the floor several times during close exchanges.
Parker closed well, but several stanzas were challenging to assess. However, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Hatton Homage Motivates Manchester Derby Contest
In the co-main event, Arthur defeated Rea by divided decision in a excellent all-Manchester battle to win the European light heavyweight championship.
The venue fell silent for a profoundly moving memorial prior to the bout as 10 bells rang in honor of the city's native Hatton, who succumbed at age 46 in September.
It was the premier televised match card in the urban center since Hatton's death. As the last bell faded, the silence became a roar of "there's just one Hatton".
The action within the ring equaled the feeling. The eventual winner was sent to the canvas by a powerful punch flush on the jaw in the early round, standing uncertainly to his footing on the eight count.
But the Manchester United-red shorts of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was marked up early, significant bruising developing under his orbital area as the fighters exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the intensity hardly diminished over 12 rounds.
Arthur barely secured the verdict with official scores of even score, narrow lead and wider gap, but both fighters were determined and courageous, everything their idol Hatton embodied.
