British light-heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive ten-round fight at the boxing arena.
But the challenger landed significant shots, landing some telling single shots in a fight where the styles didn't complement each other, with frequent clinching disrupting the contest.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my finest performance but what do champions do? They succeed," the victor said in the arena as he was met by disapproval from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts felt the challenger, 31, deserved the decision but the Derbyshire fighter experienced the second setback of his 28-match professional journey.
The Champion Claims Win in Dull Match
Buatsi's progress has plateaued in recent years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the next star of British boxing, he now finds himself trying to realize his potential - possibly in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter ready to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after breaking his hand in the contest, was making just his second fight at light-heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a protective stance to narrowly win the better rounds.
The crowd's patience diminished during regular grabbing, with the challenger slipping to the canvas various instances during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. Although, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
Buatsi progresses, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Tribute Fuels Local Rivalry Contest
In the supporting bout, Arthur overcame Rea by divided decision in a excellent local rivalry fight to capture the European light heavyweight championship.
The arena became quiet for a extremely emotional tribute ahead of the contest as ten bells sounded in honor of the city's native Hatton, who passed away aged 46 in September.
It was the first major televised fight night in the city since Hatton's death. As the final chime faded, the stillness became a roar of "there's just one Ricky Hatton".
The fighting during the bout equaled the feeling. The eventual winner was sent to the canvas by a left hook squarely on the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored attire of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was marked up soon, heavy swelling forming under his face as the pair exchanged punishing blows.
Rea, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the intensity seldom decreased over the full distance.
The victor edged the decision with scoring tallies of 114-114, narrow lead and 115-112, but the two athletes were relentless and full of heart, everything their idol Hatton represented.
