British light-heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive 10-round contest at the Co-op Live Arena.
But the challenger had his moments, landing some telling single shots in a fight where the approaches didn't complement each other, with excessive holding disrupting the fight.
The scoring judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," the victor said in the ringside as he was met by negative reactions from the spectators.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Various analysts believed the challenger, 31, should have been awarded the decision but the Derbyshire fighter experienced the second defeat of his 28-match professional journey.
Buatsi Claims Victory in Dull Encounter
The fighter's advancement has slowed in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what appears to be a last chance - under recent support.
He started carefully, with neither fighter willing to overcommit in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after damaging his hand during the bout, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who worked behind a protective stance to narrowly win the better stanzas.
The spectators' acceptance wore thin amid frequent holding, with the challenger falling to the floor various instances during close exchanges.
The underdog ended stronger, but multiple periods were hard to judge. Although, previous titleholder Carl Frampton - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the likes of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Tribute Inspires Manchester Derby Battle
In the secondary fight, Arthur overcame Rea by split-decision in a terrific Manchester vs Manchester contest to capture the European light-heavyweight championship.
The venue grew hushed for a deeply poignant memorial prior to the bout as ten bells sounded in honor of the city's native Ricky Hatton, who died aged 46 in recently.
It was the first major televised match card in the city since Hatton's death. As the concluding sound faded, the quiet became a shout of "only one Hatton".
The competition within the ring reflected the sentiment. Arthur was sent to the canvas by a powerful punch squarely on the chin in the early round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red shorts of Arthur soon advanced again. From the other corner, the opponent - in rival City blue - was injured quickly, noticeable damage developing under his orbital area as the fighters exchanged hard punches.
Rea, 27, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over 12 rounds.
The victor narrowly won the result with scoring tallies of 114-114, narrow lead and 115-112, but each competitor were determined and brave, everything their inspiration Hatton embodied.
