UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a close 10-round fight at the boxing arena.
But Parker had his moments, landing some telling clean blows in a contest where the techniques failed to mesh, with constant grabbing spoiling the contest.
Two judges had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my best showing but what do champions do? They succeed," the victor commented in the ringside as he was faced disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th career victory.
Several boxing experts believed the challenger, 31, should have been awarded the decision but the contender endured the second loss of his 28-fight career.
The Champion Secures Win in Dull Affair
His career development has stalled in recent years through contract problems and long spells of inactivity.
Once tipped as the rising talent of UK boxing, he now stands trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors ready to take risks in a calculated initial rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who utilized a tight guard to narrowly win the better periods.
The audience's tolerance diminished amid frequent holding, with Parker going down various instances during close exchanges.
Parker finished the stronger, but many rounds were hard to judge. However, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor moves on, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Homage Motivates Manchester Derby Fight
In the supporting bout, Arthur beat Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to win the continental belt.
The arena fell silent for a extremely emotional homage ahead of the contest as 10 bells sounded in memory of local hero Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised boxing event in the city since Hatton's death. As the concluding sound ended, the stillness transitioned to a shout of "only one Hatton".
The competition during the bout reflected the emotion. Arthur was knocked down by a significant blow directly to the face in the early round, getting up unsteadily to his feet on the eight count.
But the red-colored shorts of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was marked up quickly, significant bruising forming under his face as the fighters landed powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity hardly diminished over twelve rounds.
The victor edged the result with scoring tallies of draw, narrow lead and wider gap, but the two athletes were determined and courageous, all the qualities their hero the legend represented.
