British light heavyweight Joshua Buatsi made a winning yet unimpressive start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a close ten-round contest at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful individual punches in a fight where the techniques failed to mesh, with excessive holding spoiling the action.
The officials judged it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my finest display but how do champions respond? They prevail," the victor commented in the ring as he was greeted with boos from the spectators.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts felt Parker, 31, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-match career.
Buatsi Earns Win in Uneventful Affair
Buatsi's progress has stalled in recent times through management issues and considerable time of lack of fights.
Once tipped as the future of UK boxing, he now finds himself trying to realize his potential - possibly in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with both competitors ready to overcommit in a calculated initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, causing problems for the favorite, who worked behind a tight guard to edge the better rounds.
The spectators' acceptance diminished amid constant clinching, with Parker falling to the floor various instances during grappling.
The underdog finished the stronger, but many rounds were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - on this evidence - still appears challenging.
Hatton Homage Fuels All-Manchester Battle
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a terrific Manchester vs Manchester fight to capture the European light heavyweight belt.
The arena fell silent for a profoundly moving homage prior to the bout as a bell ceremony rang in honor of local hero Hatton, who died aged 46 in September.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the last bell faded, the quiet gave way to a shout of "there's only one Hatton".
The fighting during the bout matched the sentiment. Arthur was sent to the canvas by a powerful punch squarely on the chin in the initial stage, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, Rea - in competitive blue - was damaged quickly, noticeable damage developing under his orbital area as the pair traded hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over 12 rounds.
Arthur narrowly won the verdict with official scores of even score, 115-113 and wider gap, but both fighters were relentless and courageous, all the qualities their inspiration Hatton represented.
