UK light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a tight 10-round contest at the boxing arena.
But Parker had his moments, connecting with powerful individual punches in a fight where the styles never quite clicked, with frequent clinching marring the contest.
The officials scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi stated in the arena as he was greeted with negative reactions from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in February - to earn a 20th career victory.
Several boxing experts thought Parker, 31, merited the victory but the contender suffered the second setback of his 28-fight professional journey.
The Champion Secures Victory in Slow Match
The fighter's advancement has stalled in recent times through contract problems and long spells of lack of fights.
Once tipped as the next star of the British fight scene, he now stands trying to fulfil that early promise - possibly in what appears to be a last chance - under fresh management.
He opened tentatively, with the two boxers ready to overcommit in a cagey early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for Buatsi, who operated with a solid defense to edge the more effective stanzas.
The spectators' acceptance diminished amid frequent holding, with the challenger slipping to the canvas several times during grappling.
The underdog finished the stronger, but many rounds were hard to judge. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor moves on, but with the likes of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires All-Manchester Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a excellent Manchester vs Manchester battle to secure the European light heavyweight title.
The venue fell silent for a profoundly moving homage before the fight as ten bells sounded in honor of Manchester's own Ricky Hatton, who passed away at age 46 in recently.
It was the premier televised fight night in the city since the passing of Hatton. As the final chime disappeared, the silence transitioned to a roar of "there's only one Ricky Hatton".
The fighting during the bout matched the emotion. Arthur was floored by a left hook squarely on the face in the early round, rising shakily to his footing on the referee's count.
But the traditional red attire of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was injured early, significant bruising appearing under his face as the duo exchanged hard punches.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the action hardly diminished over 12 rounds.
Arthur barely secured the decision with scoring tallies of even score, narrow lead and clearer margin, but both fighters were relentless and courageous, exactly what their hero the legend embodied.
