British light heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a competitive 10-round bout at the Manchester venue.
But Parker found success, delivering effective single shots in a match where the styles didn't complement each other, with constant grabbing disrupting the contest.
Two judges scored it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my best showing but what defines champions? They succeed," Buatsi stated in the arena as he was met by disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers believed Parker, 31, deserved the victory but the British boxer suffered the second defeat of his 28-match career.
The Champion Claims Victory in Uneventful Affair
The fighter's advancement has stalled in recent times through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors willing to overcommit in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who worked behind a protective stance to narrowly win the more effective stanzas.
The crowd's patience diminished during regular grabbing, with the challenger going down multiple occasions during close exchanges.
The underdog closed well, but several stanzas were hard to judge. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
The victor advances, but with the presence of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the secondary fight, Arthur defeated Rea by split-decision in a terrific local rivalry fight to secure the European light-heavyweight title.
The stadium fell silent for a extremely emotional tribute ahead of the contest as a bell ceremony rang in honor of local hero Hatton, who passed away at age 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the concluding sound faded, the stillness transitioned to a roar of "there's only one Hatton".
The fighting inside the ropes equaled the emotion. Arthur was floored by a left hook flush on the face in the initial stage, standing uncertainly to his footing on the referee's count.
But the traditional red equipment of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was marked up early, heavy swelling forming under his orbital area as the fighters exchanged hard punches.
Rea, twenty-seven, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the intensity seldom decreased over twelve rounds.
Arthur narrowly won the result with judges scorecards of even score, close margin and wider gap, but both fighters were relentless and full of heart, everything their idol Hatton represented.
