UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a tight ten-round bout at the Manchester venue.
But Parker found success, delivering effective single shots in a contest where the approaches didn't complement each other, with excessive holding spoiling the fight.
Two judges scored it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my finest performance but how do champions respond? They succeed," Buatsi stated in the ring as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his initial pro loss - an epic battle with his previous opponent in last winter - to secure a 20th career victory.
Various analysts thought the challenger, thirty-one, merited the win but the Derbyshire fighter experienced the second defeat of his 28-fight career.
Buatsi Earns Triumph in Uneventful Match
His career development has slowed in recent times through promotional disputes and long spells of lack of fights.
Previously predicted as the next star of UK boxing, he now stands trying to realize his potential - possibly in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with both competitors prepared to be aggressive in a tentative opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after breaking his hand during the bout, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, Parker had kept it close, causing problems for the favorite, who worked behind a solid defense to barely take the better periods.
The crowd's patience wore thin amid regular grabbing, with the challenger slipping to the canvas several times during grappling.
Parker finished the stronger, but several stanzas were hard to judge. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just a single round.
The victor moves on, but with the likes of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Hatton Homage Motivates Local Rivalry Fight
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a excellent Manchester vs Manchester battle to secure the continental championship.
The venue grew hushed for a profoundly moving tribute before the fight as 10 bells tolled in memory of the city's native Ricky Hatton, who succumbed 46 years old in September.
It was the first major televised fight night in the location since the passing of Hatton. As the final chime ended, the silence became a shout of "only one Ricky Hatton".
The competition inside the ropes matched the feeling. Arthur was knocked down by a left hook squarely on the face in the early round, standing uncertainly to his position on the count of eight.
But the traditional red attire of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was marked up early, heavy swelling appearing under his face as the fighters landed hard punches.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with effective uppercuts as the action seldom decreased over twelve rounds.
The victor edged the verdict with official scores of even score, 115-113 and 115-112, but both fighters were relentless and brave, all the qualities their hero Hatton represented.
