UK light-heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a majority decision in a tight ten-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a contest where the approaches failed to mesh, with constant grabbing marring the action.
The officials had it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They succeed," Buatsi stated in the arena as he was met by disapproval from the audience.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts thought Parker, 31, should have been awarded the win but the British boxer experienced the second loss of his 28-bout professional journey.
The Champion Earns Victory in Uneventful Match
Buatsi's progress has plateaued in recent years through management issues and considerable time of inactivity.
Once tipped as the future of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers willing to be aggressive in a calculated early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second bout at light heavyweight.
By the middle rounds, Parker had made it competitive, causing problems for Buatsi, who operated with a protective stance to narrowly win the better stanzas.
The spectators' acceptance wore thin during frequent holding, with the challenger going down multiple occasions during grappling.
The underdog closed well, but many rounds were difficult to score. However, ex-champion the boxing analyst - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just one round.
Buatsi advances, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Homage Motivates Local Rivalry Contest
In the co-main event, Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to secure the continental championship.
The stadium grew hushed for a extremely emotional homage before the fight as a bell ceremony sounded in memory of Manchester's own Hatton, who succumbed 46 years old in recently.
It was the premier televised match card in the location since Hatton's death. As the last bell disappeared, the stillness became a roar of "there's only one Hatton".
The action within the ring equaled the sentiment. The eventual winner was floored by a powerful punch squarely on the jaw in the early round, rising shakily to his position on the count of eight.
But the red-colored equipment of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was damaged early, heavy swelling developing under his eye as the duo landed hard punches.
Rea, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace seldom decreased over twelve rounds.
Arthur barely secured the decision with judges scorecards of 114-114, close margin and 115-112, but each competitor were persistent and full of heart, all the qualities their idol Hatton stood for.
