UK light heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a majority decision in a close 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a contest where the styles didn't complement each other, with frequent clinching spoiling the contest.
Two judges had it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my finest showing but what do champions do? They succeed," Buatsi said in the arena as he was met by disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Several boxing experts thought the challenger, 31, should have been awarded the win but the British boxer suffered the second setback of his 28-match career.
Buatsi Claims Triumph in Slow Affair
The fighter's advancement has stalled in recent years through management issues and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under recent support.
He started carefully, with neither fighter prepared to overcommit in a calculated initial rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second bout at the higher weight class.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who worked behind a solid defense to barely take the more effective rounds.
The crowd's patience wore thin because of frequent holding, with the challenger going down several times during clinches.
Parker closed well, but multiple periods were difficult to score. Although, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Inspires Local Rivalry Battle
In the co-main event, Arthur overcame Bradley Rea by split-decision in a outstanding local rivalry battle to capture the European light-heavyweight title.
The arena became quiet for a extremely emotional tribute prior to the bout as a bell ceremony sounded in honor of Manchester's own Hatton, who passed away at age 46 in September.
It was the premier televised match card in the urban center since Hatton's passing. As the concluding sound ended, the silence became a chant of "there's just one Hatton".
The action during the bout reflected the sentiment. The eventual winner was sent to the canvas by a left hook squarely on the face in the initial stage, standing uncertainly to his footing on the eight count.
But the traditional red shorts of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was marked up early, heavy swelling forming under his eye as the duo traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the intensity hardly diminished over the full distance.
Arthur narrowly won the verdict with scoring tallies of draw, close margin and wider gap, but the two athletes were relentless and brave, exactly what their inspiration Hatton embodied.
