UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round bout at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a contest where the styles didn't complement each other, with excessive holding disrupting the action.
The officials scored it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest showing but what do champions do? They win," the victor stated in the ringside as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers thought the challenger, thirty-one, deserved the victory but the Derbyshire fighter endured the second loss of his 28-fight career.
The Champion Claims Win in Uneventful Affair
Buatsi's progress has stalled in the past few years through contract problems and considerable time of lack of fights.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers prepared to overcommit in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a tight guard to barely take the better stanzas.
The crowd's patience diminished during frequent holding, with Parker falling to the floor various instances during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Fight
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a excellent all-Manchester contest to win the continental title.
The arena became quiet for a profoundly moving tribute ahead of the contest as 10 bells rang in remembrance of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the first major televised fight night in the location since Hatton's passing. As the final chime disappeared, the stillness became a shout of "there's just one Hatton".
The action during the bout reflected the feeling. Arthur was floored by a powerful punch directly to the chin in the early round, getting up unsteadily to his position on the referee's count.
But the traditional red equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in competitive blue - was marked up soon, heavy swelling appearing under his face as the fighters traded punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the intensity rarely dropped over 12 rounds.
Arthur narrowly won the verdict with judges scorecards of even score, close margin and wider gap, but each competitor were relentless and full of heart, everything their inspiration Hatton stood for.
