UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a close 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the approaches failed to mesh, with excessive holding disrupting the contest.
The scoring judges scored it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi commented in the arena as he was met by disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers felt Parker, thirty-one, merited the win but the contender experienced the second setback of his 28-fight professional journey.
The Champion Secures Win in Uneventful Affair
Buatsi's progress has plateaued in the past few years through management issues and extended periods of lack of fights.
Earlier forecast as the next star of British boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors ready to be aggressive in a calculated opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to edge the cleaner stanzas.
The audience's tolerance decreased amid frequent holding, with Parker slipping to the canvas several times during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. Although, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Homage Fuels All-Manchester Fight
In the supporting bout, Arthur overcame Rea by close verdict in a outstanding local rivalry contest to win the European light heavyweight belt.
The venue became quiet for a extremely emotional memorial ahead of the contest as 10 bells tolled in remembrance of local hero Hatton, who died at age 46 in last month.
It was the premier televised fight night in the location since Hatton's death. As the last bell faded, the stillness became a shout of "only one Hatton".
The competition inside the ropes matched the feeling. The eventual winner was sent to the canvas by a powerful punch squarely on the chin in the early round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was damaged early, heavy swelling forming under his orbital area as the duo traded punishing blows.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with stinging uppercuts as the pace hardly diminished over the full distance.
Arthur narrowly won the decision with scoring tallies of draw, 115-113 and 115-112, but each competitor were determined and full of heart, exactly what their hero the legend stood for.
