UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a competitive 10-round fight at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a match where the approaches failed to mesh, with frequent clinching marring the fight.
The scoring judges scored it 96-94 for to Buatsi, with the third a even score.
"It wasn't my best performance but what do champions do? They prevail," Buatsi commented in the ringside as he was met by boos from the audience.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers thought the challenger, 31, merited the decision but the British boxer endured the second setback of his 28-match professional journey.
The Champion Earns Victory in Slow Match
Buatsi's progress has stalled in recent years through management issues and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to achieve expectations - possibly in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers willing to be aggressive in a calculated opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was making just his second appearance at light heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who utilized a protective stance to barely take the cleaner stanzas.
The crowd's patience wore thin amid frequent holding, with the challenger falling to the floor several times during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor progresses, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Hatton Tribute Fuels Local Rivalry Fight
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a outstanding all-Manchester fight to capture the European light-heavyweight championship.
The venue fell silent for a extremely emotional tribute ahead of the contest as 10 bells sounded in remembrance of local hero Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast match card in the city since Hatton's passing. As the final chime faded, the silence transitioned to a shout of "there's only one Hatton".
The fighting during the bout reflected the emotion. The eventual winner was floored by a left hook directly to the jaw in the initial stage, standing uncertainly to his position on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. From the other corner, the opponent - in opposing blue - was marked up soon, significant bruising forming under his eye as the duo landed hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the action seldom decreased over the full distance.
Arthur narrowly won the result with scoring tallies of draw, close margin and wider gap, but each competitor were relentless and full of heart, everything their inspiration Hatton embodied.
