UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive ten-round fight at the boxing arena.
But the challenger landed significant shots, landing some telling clean blows in a match where the techniques failed to mesh, with frequent clinching marring the contest.
Two judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but what do champions do? They succeed," Buatsi stated in the ring as he was faced disapproval from the crowd.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Several boxing experts thought Parker, 31, merited the decision but the British boxer suffered the second defeat of his 28-bout professional journey.
Buatsi Secures Triumph in Dull Affair
Buatsi's progress has stalled in recent times through management issues and considerable time of inactivity.
Once tipped as the next star of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter ready to take risks in a calculated early stages.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the cleaner periods.
The audience's tolerance wore thin amid constant clinching, with the challenger going down various instances during clinches.
The underdog ended stronger, but many rounds were hard to judge. Nevertheless, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Fuels Manchester Derby Contest
In the co-main event, Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry fight to capture the European light-heavyweight title.
The arena became quiet for a deeply poignant homage prior to the bout as 10 bells rang in memory of local hero Ricky Hatton, who died 46 years old in September.
It was the premier televised boxing event in the urban center since Hatton's death. As the last bell ended, the quiet gave way to a chant of "only one Ricky Hatton".
The fighting during the bout equaled the feeling. Arthur was knocked down by a significant blow squarely on the jaw in the initial stage, standing uncertainly to his position on the referee's count.
But the traditional red equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was marked up soon, significant bruising forming under his orbital area as the fighters traded punishing blows.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over the full distance.
Arthur barely secured the result with official scores of draw, 115-113 and clearer margin, but each competitor were relentless and brave, exactly what their inspiration the legend represented.
