British light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a tight ten-round fight at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a fight where the approaches didn't complement each other, with constant grabbing marring the fight.
Two judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my finest showing but what defines champions? They prevail," Buatsi stated in the ring as he was greeted with boos from the audience.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Various analysts believed Parker, thirty-one, deserved the win but the Derbyshire fighter endured the second loss of his 28-match career.
The fighter's advancement has stalled in the past few years through management issues and long spells of lack of fights.
Previously predicted as the future of UK boxing, he now is positioned trying to realize his potential - possibly in what seems like a last chance - under recent support.
He opened tentatively, with the two boxers prepared to take risks in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand mid-fight, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had made it competitive, causing problems for the favorite, who worked behind a solid defense to edge the better rounds.
The spectators' acceptance decreased during constant clinching, with Parker going down several times during grappling.
Parker closed well, but several stanzas were challenging to assess. Although, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
Buatsi advances, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
In the co-main event, Arthur defeated Rea by split-decision in a excellent local rivalry battle to secure the European light heavyweight belt.
The venue became quiet for a profoundly moving homage before the fight as 10 bells tolled in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised boxing event in the city since Hatton's passing. As the final chime ended, the quiet became a roar of "there's only one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was knocked down by a left hook squarely on the face in the second round, rising shakily to his position on the count of eight.
But the traditional red equipment of the fighter soon came forward again. From the other corner, the opponent - in competitive blue - was marked up quickly, heavy swelling forming under his eye as the pair traded hard punches.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over the full distance.
Arthur edged the result with official scores of 114-114, 115-113 and clearer margin, but both fighters were relentless and brave, everything their inspiration the legend represented.
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