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 medal winner's activity level seemingly secured him a split decision in a competitive 10-round bout at the Manchester venue.
But Parker found success, delivering effective single shots in a match where the techniques failed to mesh, with excessive holding disrupting the action.
Two judges judged it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best showing but what do champions do? They succeed," the victor stated in the ringside as he was met by boos from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to secure a 20th pro success.
Several boxing experts felt Parker, thirty-one, merited the win but the contender suffered the second loss of his 28-match career.
The Champion Earns Win in Dull Match
Buatsi's progress has slowed in recent times through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a last chance - under new promotional backing.
He opened tentatively, with both competitors ready to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who operated with a protective stance to edge the more effective stanzas.
The spectators' acceptance decreased amid constant clinching, with Parker falling to the floor several times during close exchanges.
The underdog closed well, but many rounds were hard to judge. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Memorial Inspires All-Manchester Contest
In the secondary fight, Arthur defeated Rea by close verdict in a excellent all-Manchester contest to secure the European light heavyweight belt.
The venue became quiet for a deeply poignant memorial ahead of the contest as 10 bells sounded in remembrance of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised match card in the urban center since Hatton's passing. As the final chime faded, the silence became a roar of "only one Hatton".
The action within the ring matched the feeling. Arthur was floored by a powerful punch directly to the face in the initial stage, rising shakily to his feet on the referee's count.
But the red-colored attire of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was marked up soon, heavy swelling forming under his face as the pair landed powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with effective uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the verdict with official scores of 114-114, close margin and 115-112, but both fighters were relentless and courageous, exactly what their hero the legend embodied.
