British light-heavyweight Joshua Buatsi earned a win yet disappointing debut to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a close 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective individual punches in a contest where the styles didn't complement each other, with constant grabbing disrupting the fight.
Two judges had it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my best showing but what defines champions? They succeed," Buatsi commented in the ring as he was greeted with negative reactions from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a 20th pro success.
Several boxing experts believed Parker, thirty-one, merited the decision but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
Buatsi Claims Triumph in Uneventful Match
Buatsi's progress has plateaued in recent times through contract problems and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - perhaps in what appears to be a last chance - under recent support.
He opened tentatively, with both competitors ready to overcommit in a cagey initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second bout at light-heavyweight.
By the halfway stage, Parker had made it competitive, making life awkward for the favorite, who worked behind a tight guard to narrowly win the better stanzas.
The audience's tolerance decreased during constant clinching, with the challenger going down various instances during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. However, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor moves on, but with the presence of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Hatton Memorial Fuels All-Manchester Fight
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a excellent Manchester vs Manchester battle to capture the continental belt.
The arena became quiet for a profoundly moving memorial prior to the bout as a bell ceremony tolled in memory of local hero Ricky Hatton, who passed away 46 years old in last month.
It was the first major televised fight night in the urban center since Hatton's death. As the final chime disappeared, the silence became a roar of "there's just one Ricky Hatton".
The action inside the ropes matched the feeling. Arthur was floored by a significant blow directly to the chin in the early round, getting up unsteadily to his position on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was injured soon, noticeable damage forming under his orbital area as the duo landed powerful shots.
Rea, 27, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the pace seldom decreased over the full distance.
Arthur barely secured the result with official scores of draw, close margin and 115-112, but both fighters were persistent and courageous, all the qualities their idol the legend embodied.
