UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive 10-round bout at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a fight where the approaches failed to mesh, with frequent clinching spoiling the fight.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but how do champions respond? They prevail," the victor said in the ringside as he was greeted with boos from the audience.
The British fighter got back to winning after his first professional defeat - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Some ringside observers believed the challenger, thirty-one, merited the victory but the Derbyshire fighter experienced the second defeat of his 28-fight career.
The Champion Claims Victory in Slow Encounter
Buatsi's progress has stalled in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under recent support.
He began cautiously, with the two boxers prepared to be aggressive in a tentative initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second bout at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who utilized a tight guard to barely take the cleaner stanzas.
The spectators' acceptance diminished during frequent holding, with the challenger going down several times during grappling.
The underdog closed well, but many rounds were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Homage Inspires Local Rivalry Contest
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a terrific Manchester vs Manchester fight to capture the European light-heavyweight title.
The stadium fell silent for a profoundly moving memorial before the fight as a bell ceremony rang in memory of local hero Hatton, who succumbed at age 46 in recently.
It was the premier televised match card in the location since Hatton's passing. As the final chime ended, the stillness became a shout of "there's only one Hatton".
The competition inside the ropes equaled the feeling. The eventual winner was floored by a left hook directly to the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the traditional red attire of the fighter soon came forward again. On the opposite side, Rea - in opposing blue - was injured quickly, heavy swelling forming under his eye as the duo traded punishing blows.
The challenger, 27, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the action hardly diminished over the full distance.
Arthur barely secured the verdict with judges scorecards of draw, narrow lead and wider gap, but each competitor were determined and brave, all the qualities their hero the legend embodied.
