UK light heavyweight Joshua Buatsi made a winning yet disappointing start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive 10-round fight at the Manchester venue.
But the challenger landed significant shots, delivering effective individual punches in a fight where the techniques failed to mesh, with constant grabbing marring the action.
The officials had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but what defines champions? They prevail," the victor said in the arena as he was met by negative reactions from the spectators.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to claim a 20th career victory.
Several boxing experts felt Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
Buatsi Secures Win in Slow Encounter
Buatsi's progress has slowed in recent times through promotional disputes and extended periods of lack of fights.
Previously predicted as the future of British boxing, he now stands trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter prepared to take risks in a tentative opening few rounds.
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 appearance at light-heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for the favorite, who worked behind a tight guard to barely take the more effective stanzas.
The crowd's patience decreased because of regular grabbing, with the challenger falling to the floor several times during grappling.
Parker closed well, but several stanzas were hard to judge. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter Benavidez, and Russian star Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Tribute Motivates Local Rivalry Contest
In the co-main event, Arthur beat Bradley Rea by close verdict in a terrific local rivalry contest to secure the continental title.
The arena became quiet for a profoundly moving memorial ahead of the contest as 10 bells sounded in memory of Manchester's own Ricky Hatton, who died at age 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the last bell ended, the quiet transitioned to a roar of "there's just one Hatton".
The action inside the ropes matched the feeling. The eventual winner was knocked down by a powerful punch flush on the face in the second round, getting up unsteadily to his position on the referee's count.
But the Manchester United-red equipment of Arthur soon came forward again. Across the ring, Rea - in rival City blue - was marked up quickly, noticeable damage developing under his orbital area as the pair exchanged powerful shots.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, matched the intensity with effective uppercuts as the pace hardly diminished over twelve rounds.
The victor barely secured the decision with official scores of draw, close margin and clearer margin, but the two athletes were determined and courageous, exactly what their hero the legend embodied.
