UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a tight ten-round bout at the boxing arena.
But Parker found success, delivering effective individual punches in a match where the techniques never quite clicked, with excessive holding spoiling the action.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my finest showing but what defines champions? They succeed," the victor said in the ring as he was greeted with disapproval from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, deserved the decision but the contender experienced the second setback of his 28-fight professional journey.
The Champion Secures Triumph in Dull Encounter
The fighter's advancement has stalled in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the future of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under fresh management.
He started carefully, with both competitors ready to take risks in a tentative opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after damaging his hand mid-fight, was competing in only his second bout at the higher weight class.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who utilized a protective stance to barely take the better stanzas.
The spectators' acceptance diminished because of regular grabbing, with the challenger going down various instances during clinches.
The underdog closed well, but multiple periods were difficult to score. Although, former world champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Homage Fuels Manchester Derby Fight
In the co-main event, Arthur beat Bradley Rea by divided decision in a excellent Manchester vs Manchester battle to secure the European light-heavyweight belt.
The stadium grew hushed for a extremely emotional memorial ahead of the contest as ten bells sounded in remembrance of Manchester's own Hatton, who died aged 46 in September.
It was the first major televised boxing event in the urban center since Hatton's passing. As the concluding sound disappeared, the quiet transitioned to a roar of "only one Hatton".
The competition during the bout matched the sentiment. Arthur was floored by a left hook squarely on the face in the early round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was injured soon, heavy swelling forming under his orbital area as the duo traded punishing blows.
The challenger, twenty-seven, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the pace seldom decreased over 12 rounds.
Arthur narrowly won the decision with official scores of draw, 115-113 and 115-112, but the two athletes were persistent and courageous, exactly what their idol the legend embodied.
