UK light heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a split decision in a competitive 10-round contest at the boxing arena.
But Parker had his moments, connecting with powerful single shots in a fight where the approaches didn't complement each other, with frequent clinching spoiling the contest.
Two judges scored it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my best performance but what do champions do? They prevail," the victor commented in the ring as he was met by negative reactions from the crowd.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, merited the decision but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
Buatsi Secures Victory in Slow Affair
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 - perhaps in what feels like a last chance - under fresh management.
He started carefully, with the two boxers ready to overcommit in a calculated early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was participating in his second bout at the higher weight class.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who operated with a solid defense to barely take the more effective periods.
The spectators' acceptance diminished amid frequent holding, with Parker falling to the floor multiple occasions during grappling.
Parker closed well, but multiple periods were difficult to score. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Hatton Tribute Inspires Local Rivalry Contest
In the secondary fight, Lyndon Arthur beat Rea by divided decision in a terrific Manchester vs Manchester fight to secure the European light-heavyweight belt.
The arena grew hushed for a deeply poignant memorial ahead of the contest as ten bells sounded in remembrance of local hero Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the concluding sound ended, the quiet gave way to a shout of "there's just one Ricky Hatton".
The action inside the ropes matched the sentiment. Arthur was sent to the canvas by a left hook flush on the face in the initial stage, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was injured soon, noticeable damage forming under his orbital area as the duo traded hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the action seldom decreased over twelve rounds.
The victor edged the decision with judges scorecards of even score, close margin and clearer margin, but the two athletes were relentless and brave, everything their inspiration Hatton stood for.
