UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful individual punches in a fight where the styles failed to mesh, with constant grabbing marring the fight.
Two judges scored it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but what defines champions? They win," the victor stated in the arena as he was greeted with boos from the spectators.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers felt Parker, 31, deserved the victory but the British boxer suffered the second setback of his 28-match career.
The Champion Claims Triumph in Slow Match
His career development has stalled in the past few years through contract problems and extended periods of inactivity.
Once tipped as the next star of British boxing, he now stands trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers willing to take risks in a calculated early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was making just his second bout at the higher weight class.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who worked behind a tight guard to narrowly win the better rounds.
The spectators' acceptance decreased because of frequent holding, with the challenger slipping to the canvas multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were challenging to assess. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor moves on, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Hatton Memorial Motivates Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester battle to secure the European light-heavyweight title.
The arena grew hushed for a profoundly moving homage ahead of the contest as a bell ceremony sounded in honor of Manchester's own Hatton, who died aged 46 in recently.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime ended, the quiet became a roar of "there's only one Ricky Hatton".
The competition within the ring equaled the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the face in the second round, getting up unsteadily to his position on the eight count.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was damaged early, noticeable damage forming under his orbital area as the pair landed punishing blows.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action hardly diminished over twelve rounds.
Arthur narrowly won the verdict with judges scorecards of 114-114, narrow lead and 115-112, but each competitor were relentless and full of heart, exactly what their hero the legend represented.
