British light-heavyweight Joshua Buatsi secured a victory yet disappointing beginning to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a tight ten-round fight at the boxing arena.
But Parker found success, delivering effective individual punches in a match where the approaches never quite clicked, with frequent clinching spoiling the contest.
The officials scored it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but what defines champions? They prevail," Buatsi stated in the arena as he was greeted with disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Several boxing experts thought the challenger, thirty-one, deserved the decision but the contender experienced the second defeat of his 28-bout professional journey.
Buatsi Earns Triumph in Uneventful Encounter
Buatsi's progress has plateaued in the past few years through management issues and extended periods of inactivity.
Previously predicted as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a last chance - under recent support.
He started carefully, with both competitors ready to overcommit in a cagey initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury in the contest, was competing in only his second fight at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who operated with a solid defense to narrowly win the more effective rounds.
The crowd's patience diminished amid regular grabbing, with Parker going down multiple occasions during clinches.
Parker finished the stronger, but many rounds were difficult to score. However, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the presence of power puncher Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Hatton Memorial Inspires Local Rivalry Battle
In the secondary fight, Lyndon Arthur beat Rea by split-decision in a terrific local rivalry battle to win the European light-heavyweight title.
The arena fell silent for a extremely emotional memorial prior to the bout as ten bells sounded in memory of Manchester's own Ricky Hatton, who passed away aged 46 in September.
It was the premier televised match card in the city since Hatton's passing. As the last bell ended, the quiet gave way to a chant of "only one Ricky Hatton".
The competition during the bout equaled the feeling. The eventual winner was sent to the canvas by a significant blow flush on the face in the early round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was injured quickly, significant bruising forming under his orbital area as the duo exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over the full distance.
Arthur barely secured the decision with official scores of 114-114, narrow lead and 115-112, but each competitor were relentless and courageous, everything their hero Hatton embodied.
