British light heavyweight Joshua Buatsi secured a victory yet disappointing start to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a tight ten-round fight at the Manchester venue.
But Parker found success, landing some telling individual punches in a match where the techniques didn't complement each other, with excessive holding spoiling the contest.
Two judges had it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my best display but what defines champions? They succeed," Buatsi said in the arena as he was faced boos from the spectators.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Various analysts felt Parker, thirty-one, merited the decision but the contender endured the second loss of his 28-bout career.
The Champion Claims Win in Slow Encounter
The fighter's advancement has slowed in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now stands trying to realize his potential - perhaps in what seems like a last chance - under new promotional backing.
He started carefully, with the two boxers prepared to overcommit in a cagey early stages.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who worked behind a solid defense to narrowly win the cleaner stanzas.
The spectators' acceptance diminished amid regular grabbing, with the challenger going down various instances during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. Although, former world champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Memorial Inspires All-Manchester Contest
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a excellent Manchester vs Manchester contest to win the European light-heavyweight championship.
The stadium grew hushed for a extremely emotional memorial before the fight as ten bells rang in honor of local hero Ricky Hatton, who passed away aged 46 in September.
It was the first major televised fight night in the urban center since Hatton's death. As the concluding sound faded, the quiet became a chant of "there's just one Hatton".
The action inside the ropes matched the emotion. Arthur was sent to the canvas by a powerful punch squarely on the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was damaged early, significant bruising developing under his eye as the duo landed powerful shots.
The challenger, 27, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the pace seldom decreased over 12 rounds.
Arthur edged the verdict with judges scorecards of draw, narrow lead and wider gap, but the two athletes were persistent and courageous, everything their hero Hatton embodied.
