British light heavyweight Joshua Buatsi earned a win yet disappointing beginning to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling individual punches in a contest where the approaches failed to mesh, with constant grabbing marring the fight.
The officials judged it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best performance but what defines champions? They win," Buatsi commented in the ring as he was met by disapproval from the audience.
The Londoner bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Various analysts felt Parker, 31, should have been awarded the decision but the contender suffered the second setback of his 28-bout professional journey.
Buatsi Claims Win in Slow Affair
Buatsi's progress has slowed in the past few years through management issues and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to achieve expectations - possibly in what seems like a final roll of the dice - under recent support.
He started carefully, with neither fighter ready to take risks in a calculated early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was making just his second fight at the higher weight class.
By the middle rounds, Parker had stayed in contention, causing problems for Buatsi, who operated with a protective stance to barely take the better stanzas.
The spectators' acceptance diminished during regular grabbing, with Parker falling to the floor several times during grappling.
Parker finished the stronger, but many rounds were difficult to score. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Hatton Tribute Fuels Manchester Derby Fight
In the co-main event, Arthur overcame Bradley Rea by divided decision in a outstanding Manchester vs Manchester battle to win the European light heavyweight title.
The venue fell silent for a profoundly moving homage prior to the bout as a bell ceremony rang in honor of local hero Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the final chime disappeared, the stillness gave way to a shout of "there's only one Hatton".
The action within the ring matched the sentiment. Arthur was floored by a significant blow squarely on the jaw in the initial stage, rising shakily to his position on the referee's count.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, the opponent - in rival City blue - was damaged early, noticeable damage forming under his face as the duo exchanged powerful shots.
The challenger, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
Arthur barely secured the verdict with judges scorecards of 114-114, close margin and clearer margin, but the two athletes were determined and brave, everything their inspiration Hatton represented.
