British light heavyweight Joshua Buatsi secured a victory yet disappointing start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling clean blows in a contest where the approaches failed to mesh, with constant grabbing disrupting the contest.
Two judges judged it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They prevail," the victor commented in the ringside as he was met by boos from the spectators.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts felt Parker, 31, deserved the victory but the Derbyshire fighter experienced the second setback of his 28-fight career.
Buatsi Claims Triumph in Dull Match
His career development has stalled in recent times through promotional disputes and long spells of inactivity.
Once tipped as the next star of British boxing, he now stands trying to realize his potential - possibly in what appears to be a last chance - under recent support.
He began cautiously, with neither fighter ready to take risks in a calculated initial rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was making just his second bout at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to barely take the cleaner rounds.
The spectators' acceptance decreased because of constant clinching, with the challenger falling to the floor multiple occasions during grappling.
The underdog ended stronger, but multiple periods were hard to judge. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the likes of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Motivates Local Rivalry Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a excellent local rivalry fight to capture the continental title.
The venue became quiet for a deeply poignant tribute before the fight as 10 bells rang in memory of Manchester's own Ricky Hatton, who succumbed aged 46 in September.
It was the first major televised match card in the urban center since the passing of Hatton. As the last bell ended, the silence became a chant of "there's just one Hatton".
The fighting during the bout reflected the emotion. The eventual winner was floored by a left hook squarely on the chin in the second round, getting up unsteadily to his footing on the count of eight.
But the red-colored attire of the fighter soon came forward again. From the other corner, the opponent - in competitive blue - was damaged soon, significant bruising appearing under his eye as the fighters traded powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur edged the result with judges scorecards of draw, 115-113 and wider gap, but both fighters were persistent and full of heart, all the qualities their hero the legend represented.
