UK light heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a competitive 10-round fight at the boxing arena.
But Parker landed significant shots, delivering effective single shots in a fight where the techniques never quite clicked, with frequent clinching marring the fight.
Two judges scored it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my greatest performance but how do champions respond? They succeed," Buatsi said in the ring as he was greeted with negative reactions from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers felt Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second loss of his 28-match career.
Buatsi Earns Victory in Uneventful Encounter
His career development has plateaued in recent years through management issues and considerable time of lack of fights.
Earlier forecast as the future of UK boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a last chance - under fresh management.
He began cautiously, with neither fighter ready to overcommit in a calculated opening few rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was participating in his second bout at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a solid defense to barely take the more effective stanzas.
The spectators' acceptance decreased amid frequent holding, with the challenger falling to the floor several times during clinches.
Parker closed well, but many rounds were challenging to assess. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Hatton Memorial Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to win the European light heavyweight title.
The stadium fell silent for a extremely emotional tribute ahead of the contest as ten bells rang in honor of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast fight night in the city since Hatton's death. As the concluding sound ended, the quiet became a shout of "there's only one Hatton".
The fighting within the ring matched the emotion. The eventual winner was floored by a powerful punch flush on the jaw in the early round, rising shakily to his feet on the count of eight.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was damaged quickly, heavy swelling appearing under his orbital area as the duo traded punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor edged the result with judges scorecards of even score, close margin and wider gap, but both fighters were determined and courageous, all the qualities their hero Hatton represented.
