British light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a close 10-round contest at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a fight where the approaches didn't complement each other, with excessive holding spoiling the fight.
The scoring judges had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest performance but what defines champions? They win," the victor said in the ringside as he was greeted with disapproval from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a twentieth professional win.
Various analysts believed the challenger, 31, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-bout career.
The Champion Claims Win in Slow Match
Buatsi's progress has stalled in recent times through contract problems and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what feels like a last chance - under fresh management.
He started carefully, with the two boxers willing to take risks in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who worked behind a tight guard to edge the better stanzas.
The spectators' acceptance wore thin during regular grabbing, with Parker going down various instances during close exchanges.
The underdog closed well, but multiple periods were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Hatton Memorial Fuels All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a terrific all-Manchester battle to win the continental belt.
The arena grew hushed for a extremely emotional homage ahead of the contest as ten bells sounded in honor of Manchester's own Ricky Hatton, who died at age 46 in September.
It was the first major televised fight night in the urban center since Hatton's passing. As the final chime ended, the silence gave way to a roar of "only one Hatton".
The action inside the ropes reflected the emotion. Arthur was sent to the canvas by a left hook directly to the chin in the second round, standing uncertainly to his position on the referee's count.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was injured early, heavy swelling appearing under his orbital area as the duo exchanged powerful shots.
Rea, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor barely secured the decision with scoring tallies of draw, close margin and 115-112, but each competitor were determined and courageous, all the qualities their hero Hatton embodied.
