UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a close ten-round contest at the boxing arena.
But Parker found success, connecting with powerful clean blows in a match where the styles failed to mesh, with frequent clinching disrupting the action.
Two judges judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best showing but how do champions respond? They succeed," the victor said in the ring as he was met by negative reactions from the spectators.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in February - to secure a twentieth professional win.
Various analysts thought Parker, 31, merited the victory but the contender experienced the second setback of his 28-match professional journey.
The Champion Earns Victory in Uneventful Affair
Buatsi's progress has stalled in recent times through contract problems and considerable time of lack of fights.
Previously predicted as the future of British boxing, he now is positioned trying to realize his potential - perhaps in what feels like a final roll of the dice - under recent support.
He started carefully, with both competitors prepared to be aggressive in a cagey opening few rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second appearance at light-heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to barely take the cleaner periods.
The crowd's patience decreased during regular grabbing, with Parker going down multiple occasions during close exchanges.
Parker closed well, but several stanzas were difficult to score. Although, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
The victor progresses, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - judging by this showing - still seems difficult.
Hatton Memorial Inspires Manchester Derby Battle
In the co-main event, Arthur defeated Rea by close verdict in a outstanding all-Manchester fight to secure the continental belt.
The stadium became quiet for a extremely emotional tribute prior to the bout as 10 bells tolled in remembrance of local hero Ricky Hatton, who died at age 46 in September.
It was the first major televised fight night in the location since the passing of Hatton. As the concluding sound faded, the silence gave way to a roar of "there's just one Ricky Hatton".
The competition during the bout reflected the sentiment. Arthur was floored by a left hook directly to the jaw in the initial stage, rising shakily to his feet on the eight count.
But the Manchester United-red attire of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up quickly, significant bruising appearing under his face as the pair traded hard punches.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the pace hardly diminished over 12 rounds.
The victor barely secured the verdict with judges scorecards of 114-114, 115-113 and 115-112, but the two athletes were determined and brave, exactly what their inspiration Hatton represented.
