British light-heavyweight Joshua Buatsi earned a win yet disappointing debut to life under fresh promotional backing with a points victory 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 Manchester venue.
But the challenger had his moments, connecting with powerful single shots in a contest where the techniques didn't complement each other, with excessive holding disrupting the action.
The scoring judges judged it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi stated in the ringside as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers believed Parker, 31, merited the victory but the contender endured the second setback of his 28-match career.
Buatsi Claims Victory in Dull Match
The fighter's advancement has slowed in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter willing to be aggressive in a cagey initial rounds.
Parker, 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 participating in his second bout at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for Buatsi, who worked behind a tight guard to edge the better rounds.
The crowd's patience decreased amid regular grabbing, with Parker falling to the floor various instances during grappling.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
The victor progresses, but with the likes of hard hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Hatton Memorial Inspires Local Rivalry Fight
In the supporting bout, Arthur beat Bradley Rea by close verdict in a excellent all-Manchester fight to capture the European light heavyweight championship.
The stadium became quiet for a profoundly moving memorial ahead of the contest as ten bells rang in remembrance of local hero Hatton, who passed away at age 46 in last month.
It was the premier televised match card in the location since Hatton's death. As the final chime faded, the stillness gave way to a roar of "there's just one Hatton".
The competition within the ring reflected the feeling. The eventual winner was sent to the canvas by a powerful punch flush on the jaw in the early round, rising shakily to his footing on the referee's count.
But the red-colored equipment of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was damaged quickly, heavy swelling appearing under his eye as the pair traded powerful shots.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur edged the result with judges scorecards of even score, 115-113 and wider gap, but the two athletes were determined and full of heart, all the qualities their hero the legend represented.
