UK light heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a majority decision in a tight 10-round contest at the boxing arena.
But Parker found success, connecting with powerful single shots in a match where the techniques didn't complement each other, with constant grabbing disrupting the fight.
The officials judged it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my greatest performance but how do champions respond? They prevail," Buatsi commented in the ringside as he was met by negative reactions from the audience.
The Londoner bounced back after his maiden career setback - an thrilling contest with his previous opponent in February - to claim a 20th career victory.
Several boxing experts thought the challenger, 31, merited the win but the Derbyshire fighter endured the second defeat of his 28-match career.
The Champion Claims Victory in Slow Affair
His career development has plateaued in recent years through contract problems and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter willing to take risks in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second bout at light heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who worked behind a protective stance to edge the cleaner periods.
The spectators' acceptance diminished during frequent holding, with the challenger going down multiple occasions during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi progresses, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Memorial Fuels Local Rivalry Fight
In the co-main event, Lyndon Arthur defeated Bradley Rea by split-decision in a outstanding all-Manchester battle to secure the continental title.
The arena became quiet for a deeply poignant memorial ahead of the contest as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime disappeared, the stillness gave way to a shout of "there's only one Ricky Hatton".
The fighting during the bout reflected the sentiment. Arthur was knocked down by a significant blow directly to the jaw in the second round, rising shakily to his footing on the count of eight.
But the red-colored equipment of the fighter soon came forward again. From the other corner, Rea - in opposing blue - was damaged early, heavy swelling developing under his orbital area as the duo exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the action rarely dropped over the full distance.
Arthur narrowly won the decision with scoring tallies of draw, close margin and 115-112, but the two athletes were determined and full of heart, everything their idol the legend embodied.
