UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to his career under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a competitive ten-round bout at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a contest where the styles never quite clicked, with constant grabbing disrupting the contest.
The officials judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my best display but what defines champions? They prevail," the victor stated in the arena as he was greeted with boos from the spectators.
The British fighter bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Various analysts believed the challenger, thirty-one, should have been awarded the victory but the British boxer suffered the second defeat of his 28-bout professional journey.
The Champion Claims Win in Dull Match
Buatsi's progress has slowed in recent times through management issues and long spells of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to realize his potential - possibly in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to overcommit in a cagey early stages.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand in the contest, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to barely take the more effective stanzas.
The crowd's patience diminished amid regular grabbing, with Parker falling to the floor multiple occasions during clinches.
Parker closed well, but many rounds were hard to judge. However, previous titleholder Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, giving Buatsi just a single round.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Russian champion Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Homage Inspires All-Manchester Fight
In the secondary fight, Lyndon Arthur defeated Rea by divided decision in a excellent Manchester vs Manchester fight to secure the European light heavyweight championship.
The venue fell silent for a extremely emotional homage ahead of the contest as ten bells rang in remembrance of Manchester's own Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast boxing event in the urban center since Hatton's death. As the final chime faded, the quiet gave way to a chant of "only one Ricky Hatton".
The action during the bout matched the feeling. Arthur was sent to the canvas by a powerful punch squarely on the face in the early round, standing uncertainly to his position on the referee's count.
But the traditional red shorts of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was injured early, noticeable damage developing under his orbital area as the fighters landed hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the action hardly diminished over the full distance.
Arthur narrowly won the verdict with official scores of 114-114, 115-113 and wider gap, but each competitor were persistent and brave, everything their idol the legend embodied.
