UK light heavyweight Joshua Buatsi earned a win yet disappointing start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a close 10-round bout at the boxing arena.
But Parker landed significant shots, delivering effective single shots in a contest where the approaches failed to mesh, with frequent clinching marring the contest.
The officials had it 96-94 in favor to the winner, with the third a even score.
"It wasn't my best performance but what do champions do? They prevail," the victor commented in the ringside as he was faced negative reactions from the spectators.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Several boxing experts thought the challenger, 31, should have been awarded the decision but the contender endured the second setback of his 28-bout professional journey.
Buatsi Earns Win in Dull Affair
Buatsi's progress has stalled in the past few years through management issues and extended periods of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to realize his potential - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter ready to take risks in a calculated early stages.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to edge the more effective rounds.
The crowd's patience diminished because of frequent holding, with the challenger going down several times during grappling.
Parker closed well, but many rounds were hard to judge. Although, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Memorial Fuels All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a excellent Manchester vs Manchester fight to capture the continental championship.
The stadium became quiet for a deeply poignant memorial prior to the bout as ten bells rang in remembrance of Manchester's own Ricky Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the concluding sound ended, the silence became a roar of "there's only one Hatton".
The competition within the ring reflected the feeling. Arthur was floored by a left hook flush on the face in the initial stage, getting up unsteadily to his position on the count of eight.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was marked up early, significant bruising forming under his orbital area as the pair landed hard punches.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with effective uppercuts as the pace seldom decreased over the full distance.
Arthur edged the verdict with scoring tallies of even score, close margin and clearer margin, but each competitor were relentless and full of heart, all the qualities their hero Hatton represented.
