British light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a split decision in a tight 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective single shots in a match where the techniques never quite clicked, with constant grabbing spoiling the contest.
The officials scored it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest display but how do champions respond? They succeed," the victor commented in the ring as he was faced boos from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts thought Parker, thirty-one, merited the decision but the Derbyshire fighter endured the second loss of his 28-fight career.
The Champion Earns Victory in Dull Encounter
The fighter's advancement has plateaued in recent years through management issues and extended periods of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to realize his potential - possibly in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors prepared to take risks in a calculated opening few rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who operated with a protective stance to edge the better periods.
The audience's tolerance wore thin because of frequent holding, with the challenger falling to the floor various instances during close exchanges.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian champion Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Memorial Inspires Manchester Derby Fight
In the co-main event, Arthur overcame Rea by split-decision in a outstanding all-Manchester contest to secure the European light-heavyweight title.
The venue fell silent for a deeply poignant memorial ahead of the contest as ten bells rang in memory of local hero Hatton, who succumbed at age 46 in last month.
It was the premier televised boxing event in the city since Hatton's death. As the last bell disappeared, the silence became a shout of "there's just one Ricky Hatton".
The action within the ring equaled the sentiment. Arthur was sent to the canvas by a significant blow directly to the jaw in the early round, standing uncertainly to his position on the count of eight.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was injured early, heavy swelling appearing under his eye as the pair landed punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the action rarely dropped over 12 rounds.
Arthur barely secured the verdict with official scores of even score, close margin and wider gap, but each competitor were persistent and full of heart, all the qualities their inspiration Hatton represented.
