UK light heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive ten-round bout at the Manchester venue.
But the challenger had his moments, connecting with powerful single shots in a match where the styles didn't complement each other, with constant grabbing disrupting the action.
Two judges had it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my best display but what defines champions? They win," the victor commented in the ring as he was greeted with boos from the crowd.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a 20th pro success.
Various analysts thought the challenger, thirty-one, deserved the decision but the British boxer suffered the second defeat of his 28-match professional journey.
The Champion Secures Victory in Uneventful Encounter
The fighter's advancement has stalled in the past few years through management issues and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers prepared to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who worked behind a tight guard to barely take the better stanzas.
The audience's tolerance wore thin because of frequent holding, with the challenger slipping to the canvas various instances during clinches.
Parker closed well, but several stanzas were difficult to score. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Hatton Homage Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding local rivalry battle to win the continental title.
The venue became quiet for a extremely emotional homage ahead of the contest as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who passed away 46 years old in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime disappeared, the stillness transitioned to a shout of "there's just one Hatton".
The fighting during the bout matched the sentiment. The eventual winner was knocked down by a significant blow flush on the face in the initial stage, standing uncertainly to his feet on the eight count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was injured soon, heavy swelling forming under his eye as the pair landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the action rarely dropped over the full distance.
The victor barely secured the decision with judges scorecards of draw, narrow lead and 115-112, but the two athletes were persistent and courageous, exactly what their hero Hatton represented.
