UK light heavyweight Joshua Buatsi secured a victory yet disappointing beginning to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a majority decision in a tight ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a contest where the styles failed to mesh, with constant grabbing marring the contest.
Two judges had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They win," the victor stated in the arena as he was met by disapproval from the spectators.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Several boxing experts thought the challenger, 31, merited the decision but the contender suffered the second defeat of his 28-match professional journey.
The Champion Earns Win in Dull Affair
The fighter's advancement has plateaued in recent years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the next star of the British fight scene, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers ready to overcommit in a cagey initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, creating difficulties for the favorite, who utilized a solid defense to edge the cleaner periods.
The audience's tolerance decreased during regular grabbing, with Parker going down multiple occasions during clinches.
The underdog closed well, but many rounds were challenging to assess. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Hatton Homage Motivates Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific local rivalry contest to capture the European light heavyweight belt.
The venue fell silent for a deeply poignant tribute before the fight as a bell ceremony sounded in memory of Manchester's own Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised match card in the city since Hatton's passing. As the last bell disappeared, the silence became a shout of "there's just one Ricky Hatton".
The competition within the ring matched the sentiment. The eventual winner was sent to the canvas by a powerful punch squarely on the face in the second round, standing uncertainly to his footing on the referee's count.
But the red-colored equipment of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was damaged early, significant bruising developing under his orbital area as the duo exchanged powerful shots.
Rea, 27, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor narrowly won the result with scoring tallies of 114-114, 115-113 and 115-112, but both fighters were relentless and courageous, exactly what their idol the legend stood for.
