British light-heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a close ten-round bout at the Manchester venue.
But Parker found success, landing some telling single shots in a contest where the approaches didn't complement each other, with frequent clinching disrupting the action.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but how do champions respond? They win," Buatsi commented in the arena as he was greeted with boos from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Several boxing experts felt the challenger, thirty-one, should have been awarded the victory but the British boxer endured the second setback of his 28-bout career.
The Champion Secures Triumph in Slow Affair
Buatsi's progress has plateaued in the past few years through contract problems and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now stands trying to realize his potential - possibly in what appears to be a ultimate opportunity - under recent support.
He started carefully, with neither fighter prepared to overcommit in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a tight guard to edge the more effective stanzas.
The spectators' acceptance decreased during regular grabbing, with Parker slipping to the canvas various instances during grappling.
The underdog ended stronger, but several stanzas were challenging to assess. Although, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Inspires Manchester Derby Fight
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a excellent Manchester vs Manchester contest to win the European light heavyweight championship.
The venue fell silent for a profoundly moving tribute ahead of the contest as 10 bells rang in honor of Manchester's own Hatton, who succumbed 46 years old in September.
It was the first major televised match card in the urban center since Hatton's passing. As the last bell ended, the stillness became a roar of "only one Ricky Hatton".
The action during the bout equaled the sentiment. Arthur was knocked down by a powerful punch squarely on the chin in the second round, rising shakily to his position on the count of eight.
But the traditional red shorts of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was marked up quickly, noticeable damage forming under his face as the duo traded hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with effective uppercuts as the action hardly diminished over twelve rounds.
The victor barely secured the verdict with scoring tallies of draw, narrow lead and wider gap, but each competitor were relentless and full of heart, exactly what their hero the legend embodied.
