UK light heavyweight Joshua Buatsi earned a win yet disappointing debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a close 10-round fight at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a fight where the techniques failed to mesh, with constant grabbing spoiling the fight.
The scoring judges had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my best showing but how do champions respond? They prevail," the victor said in the ring as he was met by disapproval from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, should have been awarded the win but the British boxer suffered the second loss of his 28-fight career.
The Champion Earns Triumph in Dull Match
His career development has plateaued in recent years through management issues and long spells of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under recent support.
He opened tentatively, with neither fighter ready to overcommit in a tentative opening few rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand in the contest, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for Buatsi, who worked behind a tight guard to barely take the more effective rounds.
The audience's tolerance wore thin during constant clinching, with the challenger slipping to the canvas various instances during grappling.
The underdog closed well, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Homage Motivates All-Manchester Battle
In the co-main event, Arthur beat Rea by close verdict in a outstanding Manchester vs Manchester battle to capture the European light heavyweight belt.
The stadium became quiet for a profoundly moving memorial before the fight as ten bells rang in memory of Manchester's own Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the city since the passing of Hatton. As the final chime faded, the silence transitioned to a chant of "there's only one Ricky Hatton".
The fighting within the ring reflected the sentiment. Arthur was floored by a powerful punch squarely on the face in the initial stage, standing uncertainly to his position on the eight count.
But the traditional red shorts of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged soon, significant bruising developing under his eye as the fighters landed punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the action hardly diminished over the full distance.
The victor narrowly won the result with official scores of even score, 115-113 and clearer margin, but the two athletes were determined and brave, everything their idol Hatton represented.
