UK light-heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a split decision in a close 10-round bout at the Manchester venue.
But the challenger had his moments, connecting with powerful individual punches in a match where the styles never quite clicked, with excessive holding marring the fight.
The scoring judges scored it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi said in the ring as he was met by disapproval from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Various analysts thought Parker, thirty-one, deserved the win but the contender endured the second loss of his 28-bout professional journey.
The Champion Earns Triumph in Slow Affair
The fighter's advancement has slowed in the past few years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now stands trying to achieve expectations - possibly in what seems like a final roll of the dice - under fresh management.
He started carefully, with both competitors willing to take risks in a calculated initial rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand in the contest, was making just his second appearance at light heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who worked behind a protective stance to narrowly win the better periods.
The spectators' acceptance decreased because of regular grabbing, with the challenger falling to the floor various instances during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Tribute Fuels Manchester Derby Contest
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a excellent Manchester vs Manchester contest to capture the European light heavyweight belt.
The stadium fell silent for a deeply poignant memorial before the fight as 10 bells tolled in honor of local hero Hatton, who succumbed at age 46 in last month.
It was the premier televised boxing event in the city since Hatton's passing. As the final chime ended, the stillness transitioned to a shout of "only one Ricky Hatton".
The fighting within the ring equaled the feeling. Arthur was floored by a powerful punch squarely on the face in the early round, standing uncertainly to his footing on the referee's count.
But the red-colored attire of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged soon, noticeable damage appearing under his orbital area as the fighters traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with stinging uppercuts as the action hardly diminished over the full distance.
The victor barely secured the verdict with scoring tallies of even score, narrow lead and clearer margin, but the two athletes were relentless and courageous, exactly what their hero Hatton embodied.
