British light heavyweight Joshua Buatsi secured a victory yet disappointing start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight ten-round bout at the boxing arena.
But Parker had his moments, connecting with powerful single shots in a fight where the techniques never quite clicked, with frequent clinching spoiling the action.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but what do champions do? They prevail," the victor said in the ringside as he was faced negative reactions from the audience.
The Londoner bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers felt Parker, thirty-one, merited the victory but the contender endured the second setback of his 28-match career.
The Champion Earns Victory in Uneventful Match
The fighter's advancement has stalled in recent years through contract problems and long spells of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under fresh management.
He started carefully, with both competitors ready to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who utilized a tight guard to narrowly win the more effective stanzas.
The spectators' acceptance decreased amid regular grabbing, with the challenger falling to the floor several times during clinches.
The underdog ended stronger, but several stanzas were difficult to score. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Russian champion Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Inspires Manchester Derby Fight
In the supporting bout, Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester fight to capture the continental championship.
The stadium grew hushed for a deeply poignant memorial ahead of the contest as ten bells sounded in honor of local hero Hatton, who passed away aged 46 in recently.
It was the premier televised fight night in the city since Hatton's passing. As the final chime disappeared, the stillness gave way to a shout of "only one Ricky Hatton".
The fighting inside the ropes reflected the emotion. Arthur was knocked down by a powerful punch flush on the face in the early round, rising shakily to his feet on the referee's count.
But the Manchester United-red equipment of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was damaged quickly, significant bruising appearing under his face as the fighters exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action hardly diminished over 12 rounds.
Arthur narrowly won the result with official scores of draw, 115-113 and wider gap, but both fighters were relentless and brave, everything their inspiration the legend embodied.
