UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But Parker found success, delivering effective individual punches in a contest where the approaches failed to mesh, with constant grabbing spoiling the contest.
The officials scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They win," Buatsi said in the ringside as he was met by boos from the spectators.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts thought Parker, thirty-one, deserved the victory but the contender suffered the second defeat of his 28-fight career.
Buatsi Secures Triumph in Uneventful Match
The fighter's advancement has plateaued in recent times through promotional disputes and considerable time of lack of fights.
Once tipped as the rising talent of UK boxing, he now is positioned trying to realize his potential - maybe in what feels like a final roll of the dice - under recent support.
He started carefully, with both competitors ready to overcommit in a calculated initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for Buatsi, who worked behind a solid defense to edge the more effective stanzas.
The audience's tolerance diminished during frequent holding, with Parker going down several times during close exchanges.
Parker closed well, but several stanzas were difficult to score. Nevertheless, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just one round.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Hatton Memorial Motivates Local Rivalry Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding local rivalry battle to capture the European light heavyweight title.
The arena fell silent for a deeply poignant homage ahead of the contest as a bell ceremony sounded in memory of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the last bell ended, the stillness gave way to a chant of "there's just one Ricky Hatton".
The action within the ring reflected the feeling. The eventual winner was floored by a significant blow flush on the jaw in the initial stage, standing uncertainly to his feet on the count of eight.
But the traditional red equipment of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up early, noticeable damage appearing under his face as the fighters exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over 12 rounds.
Arthur narrowly won the result with scoring tallies of draw, narrow lead and clearer margin, but the two athletes were relentless and full of heart, everything their idol the legend represented.
