UK light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive ten-round bout at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a contest where the styles never quite clicked, with excessive holding disrupting the action.
The scoring judges had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They prevail," the victor stated in the ringside as he was met by disapproval from the audience.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Some ringside observers thought Parker, 31, merited the victory but the contender experienced the second setback of his 28-bout career.
The Champion Claims Win in Dull Match
His career development has plateaued in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter ready to be aggressive in a cagey initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for the favorite, who operated with a protective stance to edge the cleaner stanzas.
The spectators' acceptance decreased because of frequent holding, with Parker going down several times during close exchanges.
The underdog closed well, but many rounds were challenging to assess. Although, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates All-Manchester Battle
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a outstanding all-Manchester contest to capture the continental title.
The venue grew hushed for a profoundly moving homage before the fight as 10 bells sounded in memory of the city's native Ricky Hatton, who died at age 46 in September.
It was the premier televised match card in the city since Hatton's passing. As the concluding sound ended, the silence gave way to a chant of "only one Ricky Hatton".
The competition inside the ropes equaled the feeling. Arthur was sent to the canvas by a powerful punch directly to the face in the second round, rising shakily to his footing on the eight count.
But the traditional red attire of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was damaged quickly, heavy swelling forming under his face as the duo traded hard punches.
Rea, 27, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the intensity hardly diminished over twelve rounds.
The victor edged the result with judges scorecards of 114-114, narrow lead and clearer margin, but the two athletes were determined and courageous, everything their inspiration Hatton embodied.
