British light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a competitive 10-round contest at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a fight where the techniques never quite clicked, with frequent clinching disrupting the contest.
The officials scored it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my best showing but how do champions respond? They win," the victor commented in the arena as he was met by disapproval from the crowd.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Some ringside observers felt Parker, thirty-one, deserved the win but the contender experienced the second setback of his 28-match professional journey.
The Champion Earns Triumph in Slow Match
The fighter's advancement has plateaued in the past few years through management issues and considerable time of lack of fights.
Previously predicted as the future of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to be aggressive in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second appearance at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to barely take the better stanzas.
The crowd's patience decreased during constant clinching, with the challenger falling to the floor various instances during clinches.
The underdog finished the stronger, but many rounds were hard to judge. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi progresses, but with the caliber of power puncher Benavidez, and Russian champion Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Hatton Homage Inspires All-Manchester Battle
In the co-main event, Arthur overcame Rea by split-decision in a terrific all-Manchester fight to win the European light-heavyweight belt.
The venue fell silent for a profoundly moving homage before the fight as ten bells sounded in remembrance of the city's native Ricky Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the final chime faded, the stillness became a shout of "only one Ricky Hatton".
The fighting during the bout reflected the feeling. The eventual winner was sent to the canvas by a powerful punch squarely on the jaw in the second round, getting up unsteadily to his feet on the eight count.
But the traditional red shorts of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was injured soon, noticeable damage forming under his face as the duo exchanged powerful shots.
Rea, 27, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace seldom decreased over twelve rounds.
The victor barely secured the verdict with scoring tallies of 114-114, narrow lead and wider gap, but the two athletes were persistent and courageous, exactly what their idol the legend embodied.
