UK light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a competitive ten-round fight at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a match where the styles never quite clicked, with frequent clinching disrupting the contest.
The scoring judges judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but what do champions do? They win," the victor stated in the ringside as he was met by disapproval from the audience.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Several boxing experts felt the challenger, 31, should have been awarded the win but the contender suffered the second loss of his 28-fight career.
Buatsi Claims Triumph in Slow Encounter
His career development has stalled in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the next star of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under recent support.
He opened tentatively, with both competitors willing to take risks in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second fight at the higher weight class.
By the middle rounds, Parker had made it competitive, causing problems for the favorite, who utilized a protective stance to edge the cleaner rounds.
The audience's tolerance wore thin during frequent holding, with the challenger slipping to the canvas several times during grappling.
Parker closed well, but many rounds were difficult to score. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Tribute Inspires Manchester Derby Fight
In the co-main event, Arthur overcame Bradley Rea by divided decision in a outstanding all-Manchester battle to capture the European light-heavyweight title.
The stadium fell silent for a profoundly moving memorial ahead of the contest as a bell ceremony tolled in remembrance of the city's native Ricky Hatton, who died at age 46 in September.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the last bell disappeared, the silence gave way to a shout of "there's only one Ricky Hatton".
The fighting during the bout matched the emotion. The eventual winner was sent to the canvas by a powerful punch flush on the chin in the early round, rising shakily to his position on the count of eight.
But the red-colored attire of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up soon, significant bruising appearing under his face as the duo traded punishing blows.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with effective uppercuts as the action hardly diminished over twelve rounds.
The victor narrowly won the result with judges scorecards of draw, 115-113 and 115-112, but the two athletes were relentless and brave, exactly what their inspiration Hatton embodied.
