UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a majority decision in a tight 10-round contest at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a fight where the styles never quite clicked, with constant grabbing disrupting the action.
The officials judged it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my finest display but how do champions respond? They win," the victor stated in the arena as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, merited the decision but the Derbyshire fighter experienced the second setback of his 28-match professional journey.
The Champion Secures Triumph in Dull Match
His career development has slowed in recent years through management issues and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers prepared to take risks in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second appearance at light-heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for Buatsi, who operated with a tight guard to edge the more effective periods.
The crowd's patience wore thin because of frequent holding, with Parker falling to the floor several times during grappling.
The underdog finished the stronger, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor progresses, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Memorial Inspires Local Rivalry Fight
In the supporting bout, Arthur overcame Rea by split-decision in a excellent all-Manchester fight to win the European light-heavyweight title.
The arena fell silent for a extremely emotional memorial ahead of the contest as ten bells tolled in honor of local hero Hatton, who passed away aged 46 in September.
It was the first major televised boxing event in the city since Hatton's death. As the last bell disappeared, the stillness became a shout of "there's only one Hatton".
The action during the bout matched the feeling. The eventual winner was floored by a significant blow flush on the chin in the second round, getting up unsteadily to his position on the eight count.
But the red-colored attire of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was injured quickly, noticeable damage developing under his eye as the fighters traded punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with effective uppercuts as the pace hardly diminished over 12 rounds.
The victor narrowly won the decision with official scores of even score, narrow lead and wider gap, but each competitor were determined and full of heart, all the qualities their idol Hatton embodied.
