British light-heavyweight Joshua Buatsi earned a win yet disappointing start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a majority decision in a close ten-round fight at the Co-op Live Arena.
But Parker found success, landing some telling single shots in a contest where the approaches failed to mesh, with excessive holding disrupting the contest.
Two judges judged it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest display but what defines champions? They succeed," Buatsi said in the ringside as he was faced disapproval from the crowd.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts believed Parker, 31, merited the victory but the British boxer experienced the second setback of his 28-bout professional journey.
His career development has slowed in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the future of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with neither fighter prepared to take risks in a cagey early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second bout at the higher weight class.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who worked behind a tight guard to barely take the better periods.
The audience's tolerance diminished because of regular grabbing, with the challenger going down several times during clinches.
The underdog closed well, but multiple periods were difficult to score. Nevertheless, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
The victor moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a excellent local rivalry contest to capture the European light-heavyweight championship.
The arena grew hushed for a profoundly moving homage before the fight as 10 bells rang in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised boxing event in the urban center since Hatton's death. As the last bell faded, the stillness transitioned to a roar of "there's only one Hatton".
The action within the ring matched the feeling. The eventual winner was sent to the canvas by a significant blow directly to the chin in the second round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was marked up early, significant bruising forming under his eye as the fighters landed hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the intensity hardly diminished over the full distance.
Arthur barely secured the verdict with judges scorecards of even score, close margin and clearer margin, but both fighters were determined and courageous, all the qualities their inspiration the legend embodied.
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