UK light heavyweight Joshua Buatsi earned a win yet underwhelming start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight 10-round bout at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a match where the styles never quite clicked, with constant grabbing marring the contest.
The scoring judges had it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my best display but what do champions do? They prevail," Buatsi commented in the arena as he was met by boos from the spectators.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, merited the win but the contender suffered the second loss of his 28-bout professional journey.
The Champion Secures Triumph in Slow Encounter
Buatsi's progress has plateaued in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of British boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a last chance - under new promotional backing.
He opened tentatively, with both competitors prepared to be aggressive in a calculated opening few rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to edge the better periods.
The crowd's patience diminished during frequent holding, with the challenger falling to the floor various instances during close exchanges.
The underdog finished the stronger, but several stanzas were hard to judge. However, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Contest
In the secondary fight, Arthur beat Bradley Rea by divided decision in a outstanding Manchester vs Manchester fight to win the European light-heavyweight title.
The stadium fell silent for a extremely emotional homage ahead of the contest as a bell ceremony sounded in honor of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the last bell faded, the silence gave way to a chant of "there's just one Hatton".
The action within the ring reflected the feeling. Arthur was knocked down by a left hook directly to the face in the initial stage, rising shakily to his position on the count of eight.
But the red-colored shorts of the fighter soon came forward again. On the opposite side, Rea - in rival City blue - was injured quickly, heavy swelling developing under his face as the duo landed punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity rarely dropped over the full distance.
The victor barely secured the verdict with scoring tallies of 114-114, narrow lead and 115-112, but the two athletes were persistent and courageous, everything their hero the legend represented.
