UK light-heavyweight Joshua Buatsi made a winning yet disappointing start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But Parker found success, delivering effective single shots in a contest where the techniques didn't complement each other, with frequent clinching disrupting the action.
Two judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest performance but what do champions do? They prevail," Buatsi said in the arena as he was faced disapproval from the audience.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Some ringside observers felt Parker, 31, deserved the win but the Derbyshire fighter suffered the second setback of his 28-fight career.
The Champion Claims Win in Dull Match
His career development has slowed in recent years through management issues and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers ready to overcommit in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was making just his second appearance at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who worked behind a solid defense to barely take the better stanzas.
The crowd's patience diminished amid regular grabbing, with Parker going down multiple occasions during grappling.
The underdog finished the stronger, but many rounds were challenging to assess. Although, former world champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - on this evidence - still appears challenging.
Hatton Tribute Motivates All-Manchester Battle
In the secondary fight, Arthur overcame Rea by close verdict in a terrific Manchester vs Manchester fight to secure the European light-heavyweight title.
The arena grew hushed for a deeply poignant tribute before the fight as a bell ceremony rang in honor of local hero Ricky Hatton, who passed away 46 years old in recently.
It was the first major televised boxing event in the urban center since Hatton's death. As the concluding sound ended, the silence gave way to a chant of "only one Hatton".
The competition inside the ropes reflected the feeling. The eventual winner was floored by a significant blow squarely on the face in the second round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red attire of the fighter soon advanced again. On the opposite side, Rea - in rival City blue - was marked up quickly, significant bruising developing under his face as the duo traded powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the action rarely dropped over the full distance.
Arthur barely secured the decision with judges scorecards of 114-114, close margin and wider gap, but each competitor were relentless and brave, all the qualities their idol the legend embodied.
