UK light heavyweight Joshua Buatsi earned a win yet underwhelming debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a tight 10-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful individual punches in a contest where the approaches failed to mesh, with frequent clinching disrupting the fight.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my finest performance but what do champions do? They succeed," Buatsi stated in the arena as he was met by boos from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Various analysts believed the challenger, 31, should have been awarded the decision but the Derbyshire fighter experienced the second defeat of his 28-fight professional journey.
The Champion Secures Win in Uneventful Affair
The fighter's advancement has plateaued in recent times through management issues and extended periods of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to realize his potential - possibly in what feels like a last chance - under new promotional backing.
He opened tentatively, with the two boxers ready to be aggressive in a cagey opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for Buatsi, who utilized a solid defense to barely take the cleaner rounds.
The spectators' acceptance decreased amid regular grabbing, with Parker going down various instances during close exchanges.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Motivates All-Manchester Contest
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a excellent local rivalry battle to secure the European light heavyweight belt.
The arena fell silent for a profoundly moving memorial prior to the bout as 10 bells tolled in honor of the city's native Ricky Hatton, who died aged 46 in last month.
It was the first major televised boxing event in the urban center since Hatton's passing. As the final chime disappeared, the silence gave way to a chant of "there's just one Hatton".
The competition during the bout reflected the sentiment. Arthur was sent to the canvas by a significant blow directly to the face in the second round, rising shakily to his feet on the eight count.
But the Manchester United-red attire of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was damaged early, noticeable damage forming under his eye as the duo landed hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor narrowly won the decision with scoring tallies of even score, 115-113 and clearer margin, but both fighters were relentless and full of heart, all the qualities their inspiration Hatton embodied.
