UK light heavyweight Joshua Buatsi made a winning yet unimpressive debut to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a majority decision in a close 10-round fight at the Co-op Live Arena.
But Parker had his moments, connecting with powerful individual punches in a contest where the approaches failed to mesh, with constant grabbing disrupting the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my finest showing but what defines champions? They win," Buatsi commented in the ring as he was met by boos from the spectators.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to earn a 20th pro success.
Various analysts believed the challenger, thirty-one, deserved the win but the British boxer suffered the second loss of his 28-fight career.
The Champion Claims Triumph in Dull Affair
His career development has plateaued in recent years through management issues and considerable time of inactivity.
Once tipped as the next star of British boxing, he now finds himself trying to realize his potential - perhaps in what seems like a last chance - under recent support.
He opened tentatively, with both competitors prepared to take risks in a cagey initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second fight at the higher weight class.
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 cleaner periods.
The audience's tolerance wore thin because of frequent holding, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker ended stronger, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi progresses, but with the presence of power puncher Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Inspires Local Rivalry Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a excellent all-Manchester contest to capture the European light-heavyweight championship.
The venue grew hushed for a profoundly moving tribute before the fight as 10 bells sounded in memory of Manchester's own Ricky Hatton, who died 46 years old in September.
It was the first major televised match card in the city since Hatton's passing. As the last bell faded, the stillness gave way to a roar of "there's just one Ricky Hatton".
The fighting within the ring matched the emotion. The eventual winner was knocked down by a significant blow directly to the chin in the initial stage, rising shakily to his position on the referee's count.
But the red-colored equipment of the fighter soon pressed ahead again. From the other corner, Rea - in rival City blue - was marked up early, significant bruising forming under his eye as the pair landed punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the verdict with scoring tallies of draw, 115-113 and clearer margin, but both fighters were persistent and full of heart, exactly what their inspiration the legend stood for.
