UK light heavyweight Buatsi secured a victory yet unimpressive debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a close ten-round fight at the boxing arena.
But Parker found success, connecting with powerful individual punches in a match where the approaches never quite clicked, with constant grabbing marring the fight.
The scoring judges judged it 96-94 for to the winner, with the third a even score.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi commented in the arena as he was greeted with disapproval from the crowd.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts felt the challenger, thirty-one, deserved the victory but the British boxer endured the second defeat of his 28-match career.
The Champion Earns Victory in Slow Match
The fighter's advancement has plateaued in recent years through management issues and considerable time of lack of fights.
Previously predicted as the next star of British boxing, he now finds himself trying to achieve expectations - maybe in what appears to be a final roll of the dice - under recent support.
He started carefully, with both competitors prepared to overcommit in a calculated early stages.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second fight at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who operated with a solid defense to barely take the cleaner periods.
The audience's tolerance decreased during constant clinching, with Parker slipping to the canvas several times during clinches.
The underdog finished the stronger, but several stanzas were hard to judge. Although, ex-champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Tribute Inspires Local Rivalry Battle
In the co-main event, Arthur defeated Rea by divided decision in a excellent all-Manchester contest to capture the European light-heavyweight championship.
The stadium grew hushed for a extremely emotional tribute ahead of the contest as a bell ceremony tolled in honor of local hero Hatton, who succumbed at age 46 in last month.
It was the first major televised boxing event in the location since the passing of Hatton. As the final chime ended, the silence gave way to a roar of "there's just one Ricky Hatton".
The action within the ring equaled the sentiment. The eventual winner was floored by a powerful punch flush on the face in the early round, getting up unsteadily to his feet on the eight count.
But the red-colored shorts of Arthur soon came forward again. Across the ring, the opponent - in rival City blue - was injured soon, significant bruising forming under his face as the duo traded hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the action seldom decreased over 12 rounds.
Arthur barely secured the result with judges scorecards of draw, 115-113 and 115-112, but each competitor were relentless and full of heart, all the qualities their inspiration Hatton represented.
