UK light heavyweight Joshua Buatsi earned a win yet underwhelming debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a split decision in a competitive ten-round bout at the Manchester venue.
But the challenger had his moments, connecting with powerful individual punches in a fight where the approaches didn't complement each other, with excessive holding marring the contest.
Two judges judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my best showing but how do champions respond? They win," the victor stated in the arena as he was met by negative reactions from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers believed Parker, 31, deserved the decision but the British boxer suffered the second loss of his 28-fight career.
Buatsi Secures Triumph in Slow Encounter
The fighter's advancement has slowed in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a last chance - under fresh management.
He opened tentatively, with the two boxers prepared to be aggressive in a tentative early stages.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for Buatsi, who operated with a protective stance to narrowly win the more effective periods.
The spectators' acceptance diminished amid frequent holding, with the challenger going down multiple occasions during clinches.
Parker closed well, but many rounds were difficult to score. Although, ex-champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Hatton Homage Inspires All-Manchester Fight
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry battle to win the European light heavyweight championship.
The venue grew hushed for a extremely emotional homage before the fight as 10 bells rang in memory of Manchester's own Ricky Hatton, who succumbed 46 years old in September.
It was the premier televised boxing event in the location since Hatton's passing. As the final chime ended, the stillness became a chant of "there's just one Ricky Hatton".
The competition inside the ropes reflected the feeling. Arthur was sent to the canvas by a significant blow flush on the chin in the initial stage, getting up unsteadily to his position on the eight count.
But the traditional red attire of Arthur soon came forward again. Across the ring, Rea - in rival City blue - was injured early, significant bruising forming under his face as the fighters exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the pace seldom decreased over the full distance.
The victor barely secured the verdict with scoring tallies of even score, narrow lead and wider gap, but each competitor were relentless and courageous, all the qualities their hero the legend embodied.
