UK light-heavyweight Joshua Buatsi earned a win yet disappointing debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive ten-round contest at the Co-op Live Arena.
But Parker found success, delivering effective clean blows in a contest where the styles never quite clicked, with excessive holding disrupting the fight.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my best display but what do champions do? They succeed," Buatsi commented in the arena as he was greeted with negative reactions from the spectators.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers believed Parker, 31, merited the victory but the Derbyshire fighter experienced the second loss of his 28-fight career.
Buatsi Earns Win in Slow Affair
His career development has plateaued in recent times through contract problems and long spells of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to achieve expectations - possibly in what feels like a last chance - under recent support.
He opened tentatively, with both competitors willing to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second bout at light-heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who operated with a tight guard to edge the more effective periods.
The audience's tolerance decreased because of frequent holding, with Parker slipping to the canvas various instances during clinches.
The underdog closed well, but multiple periods were hard to judge. Although, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, giving Buatsi just one round.
The victor moves on, but with the presence of hard hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the co-main event, Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester fight to win the European light-heavyweight title.
The arena became quiet for a profoundly moving homage prior to the bout as ten bells sounded in memory of local hero Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the last bell disappeared, the quiet transitioned to a roar of "there's only one Ricky Hatton".
The fighting inside the ropes matched the sentiment. Arthur was floored by a powerful punch flush on the jaw in the second round, standing uncertainly to his feet on the referee's count.
But the traditional red equipment of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was injured soon, heavy swelling developing under his orbital area as the fighters traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the action hardly diminished over 12 rounds.
The victor barely secured the result with official scores of 114-114, 115-113 and wider gap, but both fighters were determined and full of heart, exactly what their idol the legend represented.
