UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close 10-round contest at the Manchester venue.
But Parker found success, landing some telling clean blows in a fight where the styles didn't complement each other, with frequent clinching spoiling the fight.
Two judges judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my best display but what defines champions? They succeed," Buatsi commented in the arena as he was greeted with disapproval from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Several boxing experts believed Parker, thirty-one, merited the decision but the British boxer endured the second loss of his 28-fight career.
Buatsi Earns Triumph in Uneventful Match
Buatsi's progress has stalled in recent times through contract problems and long spells of lack of fights.
Previously predicted as the next star of British boxing, he now is positioned trying to realize his potential - perhaps in what appears to be a last chance - under fresh management.
He opened tentatively, with neither fighter prepared to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who worked behind a protective stance to edge the more effective stanzas.
The spectators' acceptance wore thin amid frequent holding, with Parker going down various instances during close exchanges.
The underdog closed well, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor progresses, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Hatton Homage Inspires Manchester Derby Battle
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a outstanding all-Manchester battle to win the European light heavyweight belt.
The venue fell silent for a profoundly moving memorial before the fight as a bell ceremony tolled in memory of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the premier televised boxing event in the city since the passing of Hatton. As the last bell disappeared, the silence became a roar of "there's only one Hatton".
The fighting during the bout reflected the emotion. The eventual winner was knocked down by a significant blow directly to the face in the second round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, Rea - in competitive blue - was damaged early, heavy swelling forming under his orbital area as the pair landed punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the intensity hardly diminished over twelve rounds.
Arthur barely secured the verdict with scoring tallies of 114-114, 115-113 and wider gap, but the two athletes were determined and brave, everything their hero Hatton represented.
