British light-heavyweight Joshua Buatsi secured a victory yet disappointing beginning to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a competitive 10-round fight at the boxing arena.
But Parker found success, landing some telling clean blows in a fight where the styles failed to mesh, with constant grabbing marring the contest.
The officials had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but what do champions do? They win," Buatsi said in the ring as he was faced negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers thought the challenger, thirty-one, merited the win but the contender suffered the second setback of his 28-match professional journey.
Buatsi Earns Triumph in Slow Affair
The fighter's advancement has slowed in the past few years through management issues and considerable time of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to achieve expectations - maybe in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter ready to take risks in a tentative initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who operated with a protective stance to edge the better stanzas.
The crowd's patience decreased because of frequent holding, with Parker slipping to the canvas several times during close exchanges.
The underdog finished the stronger, but multiple periods were challenging to assess. However, former world champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Memorial Inspires All-Manchester Battle
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a outstanding Manchester vs Manchester battle to secure the European light-heavyweight championship.
The stadium fell silent for a deeply poignant homage before the fight as ten bells sounded in honor of the city's native Hatton, who died aged 46 in September.
It was the first major televised fight night in the location since the passing of Hatton. As the last bell ended, the stillness transitioned to a roar of "there's only one Hatton".
The fighting during the bout equaled the feeling. Arthur was sent to the canvas by a significant blow directly to the face in the initial stage, rising shakily to his position on the eight count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was injured early, heavy swelling appearing under his face as the pair traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with powerful upward punches as the intensity seldom decreased over twelve rounds.
The victor edged the decision with judges scorecards of even score, close margin and 115-112, but both fighters were persistent and courageous, all the qualities their hero Hatton embodied.
