UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close ten-round contest at the Manchester venue.
But Parker found success, delivering effective single shots in a contest where the styles failed to mesh, with excessive holding spoiling the fight.
The officials judged it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my best display but how do champions respond? They succeed," the victor commented in the ringside as he was met by disapproval from the crowd.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, deserved the decision but the contender endured the second loss of his 28-match career.
Buatsi Earns Win in Dull Encounter
His career development has slowed in recent years through management issues and extended periods of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to achieve expectations - maybe in what feels like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers ready to take risks in a cagey initial rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was making just his second bout at light-heavyweight.
By the fight's midpoint, Parker had kept it close, causing problems for the favorite, who utilized a tight guard to barely take the better periods.
The crowd's patience diminished during frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog finished the stronger, but many rounds were hard to judge. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor advances, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Inspires Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by split-decision in a terrific local rivalry fight to secure the continental championship.
The stadium became quiet for a deeply poignant memorial ahead of the contest as 10 bells sounded in honor of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised fight night in the city since Hatton's death. As the last bell disappeared, the quiet gave way to a chant of "there's just one Hatton".
The competition within the ring equaled the sentiment. Arthur was floored by a significant blow squarely on the chin in the initial stage, standing uncertainly to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was marked up early, heavy swelling forming under his eye as the pair landed powerful shots.
Rea, 27, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the action rarely dropped over twelve rounds.
The victor edged the verdict with judges scorecards of 114-114, close margin and 115-112, but each competitor were determined and brave, everything their inspiration the legend stood for.
