UK light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close 10-round fight at the Manchester venue.
But the challenger found success, connecting with powerful clean blows in a fight where the approaches failed to mesh, with excessive holding disrupting the action.
Two judges judged it 96-94 for to Buatsi, with the third a even score.
"It wasn't my best display but what defines champions? They succeed," the victor said in the ring as he was faced negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Various analysts believed the challenger, 31, deserved the victory but the contender experienced the second loss of his 28-fight professional journey.
The Champion Claims Win in Dull Encounter
Buatsi's progress has plateaued in recent times through contract problems and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now stands trying to achieve expectations - maybe in what appears to be a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers prepared to take risks in a cagey initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who utilized a tight guard to narrowly win the more effective rounds.
The spectators' acceptance wore thin during frequent holding, with Parker slipping to the canvas several times during close exchanges.
The underdog closed well, but many rounds were difficult to score. However, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Hatton Tribute Fuels Local Rivalry Fight
In the co-main event, Arthur beat Rea by close verdict in a outstanding local rivalry contest to win the European light heavyweight belt.
The venue fell silent for a deeply poignant tribute prior to the bout as 10 bells sounded in honor of the city's native Hatton, who died at age 46 in recently.
It was the first major televised match card in the urban center since the passing of Hatton. As the concluding sound disappeared, the quiet gave way to a shout of "there's just one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. Arthur was floored by a powerful punch directly to the jaw in the early round, standing uncertainly to his feet on the count of eight.
But the traditional red shorts of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was marked up soon, noticeable damage appearing under his orbital area as the fighters exchanged punishing blows.
Rea, 27, delivered effective strikes but Arthur, 34, responded in kind with effective uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the decision with judges scorecards of even score, close margin and clearer margin, but each competitor were determined and courageous, all the qualities their hero Hatton stood for.
