British light-heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But the challenger found success, connecting with powerful single shots in a match where the techniques didn't complement each other, with excessive holding disrupting the action.
The scoring judges had it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my best performance but how do champions respond? They prevail," Buatsi stated in the ringside as he was met by boos from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Various analysts thought the challenger, 31, merited the win but the contender suffered the second loss of his 28-bout professional journey.
The Champion Earns Victory in Uneventful Match
The fighter's advancement has slowed in recent years through management issues and long spells of inactivity.
Previously predicted as the rising talent of British boxing, he now stands trying to realize his potential - perhaps in what appears to be a last chance - under fresh management.
He opened tentatively, with the two boxers ready to overcommit in a calculated initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for Buatsi, who worked behind a protective stance to narrowly win the more effective stanzas.
The crowd's patience decreased amid constant clinching, with the challenger falling to the floor multiple occasions during grappling.
The underdog ended stronger, but several stanzas were challenging to assess. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates All-Manchester Contest
In the co-main event, Arthur defeated Bradley Rea by close verdict in a excellent all-Manchester fight to win the European light heavyweight title.
The arena became quiet for a profoundly moving homage before the fight as a bell ceremony sounded in memory of Manchester's own Ricky Hatton, who passed away 46 years old in last month.
It was the premier televised match card in the city since the passing of Hatton. As the final chime ended, the stillness transitioned to a chant of "there's only one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was knocked down by a significant blow squarely on the chin in the initial stage, rising shakily to his position on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was marked up soon, noticeable damage appearing under his face as the fighters exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace seldom decreased over 12 rounds.
The victor barely secured the result with judges scorecards of 114-114, narrow lead and 115-112, but each competitor were persistent and full of heart, everything their hero the legend embodied.
