British light heavyweight Joshua Buatsi made a winning yet disappointing debut to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But Parker had his moments, landing some telling individual punches in a contest where the approaches failed to mesh, with excessive holding spoiling the fight.
The scoring judges had it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my best display but what defines champions? They succeed," Buatsi commented in the arena as he was faced disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a 20th pro success.
Several boxing experts believed the challenger, thirty-one, merited the win but the British boxer endured the second setback of his 28-fight professional journey.
The Champion Secures Triumph in Dull Match
The fighter's advancement has slowed in the past few years through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to realize his potential - maybe in what appears to be a last chance - under new promotional backing.
He began cautiously, with neither fighter prepared to take risks in a cagey initial rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was making just his second bout at light heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who utilized a solid defense to narrowly win the cleaner stanzas.
The spectators' acceptance decreased during regular grabbing, with Parker going down multiple occasions during grappling.
The underdog ended stronger, but several stanzas were difficult to score. However, previous titleholder 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 moves on, but with the likes of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Homage Inspires All-Manchester Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to win the European light heavyweight championship.
The stadium grew hushed for a profoundly moving tribute prior to the bout as 10 bells sounded in honor of Manchester's own Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the final chime ended, the silence transitioned to a chant of "only one Ricky Hatton".
The action within the ring equaled the feeling. Arthur was floored by a left hook squarely on the chin in the early round, standing uncertainly to his footing on the eight count.
But the traditional red shorts of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was damaged soon, significant bruising appearing under his eye as the pair landed powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over twelve rounds.
Arthur narrowly won the result with scoring tallies of even score, close margin and wider gap, but the two athletes were persistent and courageous, all the qualities their inspiration the legend embodied.
