British light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under new promoters 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 close ten-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a contest where the styles never quite clicked, with excessive holding marring the fight.
Two judges judged it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my greatest showing but what do champions do? They succeed," the victor commented in the ring as he was greeted with boos from the crowd.
The Londoner bounced back after his initial pro loss - an epic battle with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, should have been awarded the decision but the contender experienced the second loss of his 28-match career.
The Champion Claims Triumph in Slow Affair
His career development has slowed in the past few years through contract problems and long spells of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to achieve expectations - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter ready to take risks in a tentative opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to barely take the cleaner periods.
The audience's tolerance diminished amid constant clinching, with the challenger slipping to the canvas various instances during clinches.
Parker ended stronger, but many rounds were difficult to score. However, previous titleholder the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor progresses, but with the presence of power puncher Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Contest
In the supporting bout, Arthur defeated Rea by close verdict in a terrific all-Manchester fight to win the European light heavyweight title.
The stadium became quiet for a deeply poignant tribute ahead of the contest as 10 bells rang in honor of the city's native Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised fight night in the city since Hatton's passing. As the final chime faded, the silence became a roar of "only one Hatton".
The action during the bout equaled the emotion. The eventual winner was floored by a significant blow flush on the face in the initial stage, getting up unsteadily to his position on the count of eight.
But the traditional red shorts of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was injured soon, noticeable damage forming under his orbital area as the duo traded punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over the full distance.
The victor barely secured the verdict with judges scorecards of draw, close margin and wider gap, but each competitor were relentless and brave, exactly what their idol Hatton represented.
