British light-heavyweight Joshua Buatsi secured a victory yet unimpressive debut to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a tight 10-round bout at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a match where the approaches failed to mesh, with excessive holding disrupting the fight.
The officials judged it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest showing but what defines champions? They succeed," Buatsi said in the arena as he was met by boos from the crowd.
The Londoner got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts believed Parker, 31, should have been awarded the victory but the British boxer endured the second setback of his 28-fight career.
Buatsi Secures Triumph in Slow Affair
The fighter's advancement has slowed in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers willing to be aggressive in a tentative opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was making just his second appearance at the higher weight class.
By the middle rounds, Parker had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to edge the more effective periods.
The crowd's patience decreased amid constant clinching, with Parker falling to the floor several times during grappling.
Parker closed well, but many rounds were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just one round.
The victor moves on, but with the presence of power puncher Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - judging by this showing - still seems difficult.
Hatton Tribute Inspires Local Rivalry Fight
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a excellent local rivalry fight to win the European light-heavyweight title.
The arena grew hushed for a extremely emotional homage ahead of the contest as 10 bells tolled in honor of local hero Ricky Hatton, who died aged 46 in September.
It was the first major televised match card in the location since Hatton's death. As the final chime disappeared, the quiet gave way to a shout of "there's just one Ricky Hatton".
The fighting inside the ropes matched the sentiment. Arthur was knocked down by a powerful punch flush on the jaw in the second round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was injured quickly, noticeable damage forming under his orbital area as the pair exchanged powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with effective uppercuts as the action seldom decreased over 12 rounds.
The victor barely secured the verdict with scoring tallies of 114-114, 115-113 and 115-112, but both fighters were persistent and full of heart, exactly what their hero Hatton represented.
