British light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive 10-round fight at the Manchester venue.
But the challenger landed significant shots, connecting with powerful clean blows in a match where the styles didn't complement each other, with constant grabbing marring the contest.
The scoring judges had it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my finest performance but what do champions do? They prevail," the victor commented in the ring as he was met by disapproval from the crowd.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers believed Parker, 31, merited the win but the contender endured the second defeat of his 28-fight career.
Buatsi Claims Victory in Slow Encounter
Buatsi's progress has plateaued in the past few years through promotional disputes and extended periods of lack of fights.
Previously predicted as the next star of UK boxing, he now stands trying to fulfil that early promise - maybe in what feels like a last chance - under recent support.
He started carefully, with the two boxers willing to take risks in a calculated initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was competing in only his second appearance at the higher weight class.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to barely take the more effective stanzas.
The spectators' acceptance wore thin amid frequent holding, with the challenger going down various instances during close exchanges.
Parker closed well, but multiple periods were difficult to score. Although, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Hatton Homage Fuels Manchester Derby Contest
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a outstanding local rivalry battle to capture the European light-heavyweight championship.
The venue became quiet for a extremely emotional homage before the fight as ten bells sounded in remembrance of Manchester's own Ricky Hatton, who passed away 46 years old in September.
It was the first major televised match card in the location since the passing of Hatton. As the last bell disappeared, the quiet became a shout of "there's only one Hatton".
The action inside the ropes equaled the feeling. The eventual winner was knocked down by a significant blow squarely on the face in the second round, rising shakily to his feet on the referee's count.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was injured quickly, noticeable damage developing under his orbital area as the duo traded hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the action seldom decreased over the full distance.
The victor edged the verdict with scoring tallies of even score, narrow lead and wider gap, but both fighters were relentless and brave, all the qualities their idol Hatton stood for.
