UK light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a tight 10-round fight at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a fight where the approaches never quite clicked, with excessive holding marring the fight.
Two judges had it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my finest showing but what defines champions? They win," Buatsi said in the ringside as he was met by negative reactions from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Various analysts believed the challenger, thirty-one, should have been awarded the win but the British boxer endured the second loss of his 28-bout professional journey.
The Champion Earns Win in Uneventful Match
Buatsi's progress has slowed in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under recent support.
He started carefully, with both competitors willing to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who utilized a tight guard to edge the more effective rounds.
The audience's tolerance wore thin during frequent holding, with the challenger falling to the floor several times during clinches.
The underdog finished the stronger, but several stanzas were difficult to score. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Homage Fuels Manchester Derby Contest
In the co-main event, Arthur defeated Bradley Rea by close verdict in a terrific local rivalry battle to secure the European light-heavyweight championship.
The venue became quiet for a extremely emotional tribute before the fight as 10 bells rang in remembrance of Manchester's own Hatton, who succumbed aged 46 in September.
It was the first major televised match card in the city since Hatton's passing. As the concluding sound disappeared, the quiet gave way to a chant of "there's just one Ricky Hatton".
The fighting during the bout equaled the emotion. The eventual winner was floored by a powerful punch squarely on the face in the second round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red attire of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was marked up early, significant bruising forming under his orbital area as the pair landed hard punches.
The challenger, 27, delivered effective strikes but the champion, 34, matched the intensity with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur edged the decision with official scores of draw, 115-113 and 115-112, but both fighters were persistent and full of heart, everything their idol Hatton embodied.
