UK light-heavyweight Joshua Buatsi made a winning yet unimpressive debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a tight ten-round fight at the Co-op Live Arena.
But the challenger found success, landing some telling clean blows in a match where the styles failed to mesh, with frequent clinching marring the fight.
The scoring judges had it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my best showing but what do champions do? They prevail," Buatsi commented in the ring as he was faced boos from the crowd.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Various analysts believed Parker, 31, deserved the decision but the contender endured the second setback of his 28-match professional journey.
Buatsi Secures Win in Dull Encounter
Buatsi's progress has plateaued in the past few years through promotional disputes and long spells of lack of fights.
Once tipped as the future of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter willing to overcommit in a calculated opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand during the bout, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who operated with a protective stance to edge the more effective stanzas.
The crowd's patience decreased during regular grabbing, with Parker slipping to the canvas various instances during grappling.
The underdog ended stronger, but many rounds were difficult to score. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Hatton Homage Fuels Manchester Derby Fight
In the co-main event, Arthur defeated Bradley Rea by close verdict in a terrific all-Manchester battle to capture the European light-heavyweight championship.
The arena became quiet for a extremely emotional homage prior to the bout as ten bells sounded in memory of Manchester's own Ricky Hatton, who succumbed at age 46 in recently.
It was the premier televised match card in the city since Hatton's passing. As the concluding sound ended, the quiet transitioned to a chant of "only one Hatton".
The fighting during the bout equaled the sentiment. The eventual winner was floored by a left hook directly to the chin in the early round, standing uncertainly to his footing on the referee's count.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was damaged soon, significant bruising appearing under his face as the duo landed hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor narrowly won the decision with scoring tallies of draw, 115-113 and wider gap, but both fighters were determined and brave, all the qualities their hero the legend embodied.
