UK light-heavyweight Joshua Buatsi earned a win yet disappointing start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful clean blows in a match where the styles didn't complement each other, with constant grabbing spoiling the contest.
Two judges had it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my greatest showing but what defines champions? They prevail," Buatsi said in the arena as he was greeted with negative reactions from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers believed the challenger, 31, deserved the victory but the British boxer experienced the second setback of his 28-fight career.
Buatsi Secures Win in Dull Encounter
Buatsi's progress has slowed in recent years through promotional disputes and extended periods of lack of fights.
Previously predicted as the future of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under fresh management.
He started carefully, with the two boxers willing to overcommit in a cagey early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was participating in his second appearance at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who utilized a tight guard to narrowly win the cleaner stanzas.
The crowd's patience diminished amid frequent holding, with Parker falling to the floor multiple occasions during grappling.
The underdog finished the stronger, but several stanzas were challenging to assess. However, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Hatton Memorial Motivates All-Manchester Battle
In the secondary fight, Arthur defeated Rea by divided decision in a excellent local rivalry battle to win the European light heavyweight belt.
The arena fell silent for a extremely emotional tribute ahead of the contest as ten bells tolled in remembrance of local hero Hatton, who passed away at age 46 in recently.
It was the premier televised boxing event in the location since Hatton's passing. As the final chime disappeared, the silence became a shout of "there's just one Hatton".
The action inside the ropes equaled the sentiment. Arthur was sent to the canvas by a powerful punch directly to the chin in the initial stage, rising shakily to his feet on the eight count.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was marked up soon, noticeable damage developing under his eye as the fighters exchanged hard punches.
The challenger, 27, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the intensity rarely dropped over 12 rounds.
The victor edged the verdict with official scores of even score, 115-113 and clearer margin, but both fighters were relentless and brave, everything their hero the legend represented.
