British light heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight 10-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective clean blows in a fight where the techniques failed to mesh, with constant grabbing disrupting the fight.
The scoring judges judged it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my best performance but what do champions do? They succeed," Buatsi said in the ring as he was faced negative reactions from the audience.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Several boxing experts felt Parker, 31, merited the victory but the Derbyshire fighter endured the second loss of his 28-fight career.
The Champion Earns Victory in Slow Match
Buatsi's progress has stalled in the past few years through contract problems and extended periods of inactivity.
Earlier forecast as the next star of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under recent support.
He began cautiously, with both competitors prepared to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was making just his second fight at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a protective stance to edge the better stanzas.
The spectators' acceptance decreased amid constant clinching, with Parker slipping to the canvas various instances during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi progresses, but with the caliber of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Tribute Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur beat Rea by split-decision in a terrific all-Manchester fight to capture the continental championship.
The venue fell silent for a deeply poignant tribute prior to the bout as a bell ceremony tolled in honor of the city's native Hatton, who passed away aged 46 in September.
It was the first major televised match card in the urban center since Hatton's death. As the last bell ended, the quiet became a shout of "only one Hatton".
The action during the bout reflected the sentiment. Arthur was sent to the canvas by a left hook directly to the chin in the second round, rising shakily to his feet on the eight count.
But the Manchester United-red attire of the fighter soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was injured early, significant bruising appearing under his orbital area as the pair traded hard punches.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the intensity hardly diminished over twelve rounds.
Arthur barely secured the decision with judges scorecards of draw, close margin and 115-112, but each competitor were determined and courageous, exactly what their hero the legend stood for.
