British light-heavyweight Joshua Buatsi earned a win yet underwhelming debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close ten-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective individual punches in a contest where the techniques failed to mesh, with constant grabbing marring the action.
The officials judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my best performance but what do champions do? They prevail," Buatsi commented in the ring as he was met by boos from the audience.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Several boxing experts felt the challenger, 31, merited the win but the contender suffered the second loss of his 28-bout career.
Buatsi Secures Triumph in Uneventful Encounter
The fighter's advancement has slowed in recent years through management issues and extended periods of lack of fights.
Once tipped as the next star of the British fight scene, he now stands trying to achieve expectations - possibly in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers prepared to overcommit in a tentative opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to narrowly win the cleaner stanzas.
The crowd's patience diminished during regular grabbing, with Parker going down various instances during close exchanges.
The underdog closed well, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor advances, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Battle
In the co-main event, Arthur defeated Bradley Rea by close verdict in a outstanding local rivalry contest to win the European light-heavyweight title.
The stadium grew hushed for a extremely emotional homage before the fight as ten bells rang in remembrance of the city's native Hatton, who died 46 years old in September.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the last bell ended, the stillness transitioned to a chant of "there's only one Hatton".
The action inside the ropes equaled the emotion. Arthur was knocked down by a powerful punch directly to the chin in the initial stage, rising shakily to his position on the count of eight.
But the red-colored shorts of Arthur soon advanced again. From the other corner, the opponent - in opposing blue - was marked up soon, noticeable damage forming under his face as the fighters traded powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, 34, 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 115-112, but the two athletes were determined and brave, exactly what their inspiration Hatton stood for.
