UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But Parker had his moments, delivering effective clean blows in a contest where the approaches didn't complement each other, with frequent clinching spoiling the contest.
The scoring judges judged it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my greatest performance but what do champions do? They succeed," Buatsi commented in the ringside as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Some ringside observers felt the challenger, 31, should have been awarded the victory but the contender endured the second defeat of his 28-fight professional journey.
The Champion Earns Triumph in Dull Encounter
His career development has stalled in recent years through management issues and extended periods of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to realize his potential - possibly in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter prepared to be aggressive in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was competing in only his second appearance at light heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who operated with a solid defense to barely take the more effective periods.
The audience's tolerance wore thin during regular grabbing, with Parker slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but several stanzas were challenging to assess. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Memorial Fuels Local Rivalry Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a excellent all-Manchester contest to secure the European light heavyweight championship.
The venue fell silent for a profoundly moving memorial prior to the bout as ten bells tolled in memory of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the premier televised match card in the city since the passing of Hatton. As the last bell faded, the stillness gave way to a chant of "there's only one Hatton".
The action inside the ropes matched the sentiment. The eventual winner was knocked down by a left hook directly to the jaw in the early round, standing uncertainly to his position on the eight count.
But the traditional red attire of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was injured quickly, significant bruising developing under his eye as the duo traded hard punches.
Rea, 27, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action rarely dropped over twelve rounds.
The victor narrowly won the result with official scores of even score, 115-113 and wider gap, but both fighters were relentless and courageous, exactly what their inspiration Hatton embodied.
