UK light heavyweight Joshua Buatsi secured a victory yet disappointing start to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close 10-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful clean blows in a match where the approaches never quite clicked, with constant grabbing disrupting the fight.
Two judges had it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They prevail," the victor stated in the ringside as he was met by boos from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Various analysts believed the challenger, 31, should have been awarded the decision but the contender experienced the second setback of his 28-match career.
The Champion Claims Win in Uneventful Encounter
His career development has slowed in recent times through management issues and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to realize his potential - perhaps in what appears to be a last chance - under recent support.
He opened tentatively, with both competitors willing to overcommit in a cagey initial 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 during the bout, was competing in only his second bout at light-heavyweight.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who worked behind a protective stance to edge the more effective stanzas.
The spectators' acceptance diminished because of regular grabbing, with the challenger going down multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Tribute Fuels Manchester Derby Fight
In the secondary fight, Arthur overcame Rea by close verdict in a terrific local rivalry fight to capture the European light-heavyweight championship.
The arena fell silent for a extremely emotional memorial ahead of the contest as a bell ceremony sounded in memory of the city's native Ricky Hatton, who died 46 years old in September.
It was the first major televised match card in the urban center since the passing of Hatton. As the last bell ended, the stillness transitioned to a shout of "there's only one Ricky Hatton".
The action inside the ropes reflected the feeling. The eventual winner was knocked down by a significant blow flush on the chin in the early round, rising shakily to his position on the eight count.
But the Manchester United-red attire of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was marked up early, noticeable damage appearing under his orbital area as the fighters exchanged punishing blows.
Rea, 27, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over the full distance.
The victor barely secured the decision with scoring tallies of draw, narrow lead and wider gap, but both fighters were relentless and brave, all the qualities their inspiration the legend represented.
