UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a close 10-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a contest where the styles didn't complement each other, with excessive holding disrupting the fight.
Two judges scored it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi said in the arena as he was faced disapproval from the audience.
The British fighter bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a 20th career victory.
Various analysts believed the challenger, 31, deserved the win but the contender suffered the second loss of his 28-fight career.
The Champion Earns Triumph in Slow Encounter
His career development has slowed in recent times through contract problems and extended periods of lack of fights.
Previously predicted as the future of UK boxing, he now stands trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter prepared to overcommit in a tentative opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand during the bout, was participating in his second bout at light-heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to barely take the better rounds.
The audience's tolerance wore thin amid constant clinching, with Parker slipping to the canvas various instances during close exchanges.
Parker closed well, but multiple periods were challenging to assess. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the supporting bout, Arthur beat Bradley Rea by close verdict in a excellent all-Manchester battle to capture the continental championship.
The venue grew hushed for a profoundly moving memorial ahead of the contest as ten bells rang in honor of the city's native Hatton, who died at age 46 in recently.
It was the first major televised fight night in the city since the passing of Hatton. As the last bell disappeared, the stillness transitioned to a shout of "there's only one Hatton".
The fighting inside the ropes equaled the feeling. Arthur was knocked down by a significant blow directly to the face in the early round, standing uncertainly to his footing on the count of eight.
But the traditional red equipment of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was marked up quickly, noticeable damage appearing under his face as the fighters traded punishing blows.
Rea, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with effective uppercuts as the action rarely dropped over twelve rounds.
The victor narrowly won the decision with judges scorecards of 114-114, narrow lead and clearer margin, but both fighters were determined and full of heart, all the qualities their inspiration the legend embodied.
