British light heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a competitive 10-round fight at the boxing arena.
But the challenger found success, landing some telling clean blows in a fight where the techniques failed to mesh, with constant grabbing disrupting the contest.
Two judges scored it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my finest display but what do champions do? They prevail," Buatsi stated in the arena as he was faced boos from the audience.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Some ringside observers thought Parker, thirty-one, should have been awarded the win but the British boxer experienced the second setback of his 28-fight career.
The Champion Secures Victory in Slow Affair
The fighter's advancement has stalled in recent times through contract problems and long spells of inactivity.
Previously predicted as the rising talent of British boxing, he now finds himself trying to realize his potential - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers prepared to overcommit in a cagey initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was competing in only his second appearance at light heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who utilized a protective stance to narrowly win the cleaner stanzas.
The spectators' acceptance wore thin during frequent holding, with Parker slipping to the canvas various instances during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, giving Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - judging by this showing - still seems difficult.
Hatton Memorial Inspires Manchester Derby Contest
In the supporting bout, Arthur beat Bradley Rea by split-decision in a outstanding all-Manchester fight to capture the European light heavyweight title.
The arena fell silent for a deeply poignant tribute prior to the bout as ten bells rang in memory of Manchester's own Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the final chime ended, the quiet transitioned to a shout of "only one Ricky Hatton".
The competition during the bout equaled the sentiment. The eventual winner was sent to the canvas by a powerful punch squarely on the chin in the initial stage, getting up unsteadily to his footing on the count of eight.
But the traditional red shorts of the fighter soon came forward again. Across the ring, Rea - in competitive blue - was damaged early, noticeable damage forming under his eye as the duo exchanged punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor narrowly won the decision with judges scorecards of draw, close margin and 115-112, but both fighters were persistent and full of heart, all the qualities their inspiration Hatton embodied.
