UK light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive 10-round contest at the boxing arena.
But the challenger had his moments, landing some telling individual punches in a match where the styles failed to mesh, with excessive holding marring the action.
The scoring judges judged it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my greatest performance but what do champions do? They succeed," the victor said in the arena as he was greeted with boos from the crowd.
The British fighter bounced back 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, 31, deserved the victory but the Derbyshire fighter experienced the second loss of his 28-fight career.
The Champion Claims Triumph in Uneventful Affair
Buatsi's progress has stalled in the past few years through contract problems and long spells of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to realize his potential - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with both competitors prepared to be aggressive in a tentative opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second bout at light-heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who utilized a protective stance to barely take the more effective rounds.
The spectators' acceptance decreased because of frequent holding, with Parker slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Tribute Motivates All-Manchester Battle
In the secondary fight, Lyndon Arthur defeated Rea by divided decision in a outstanding all-Manchester battle to secure the European light heavyweight title.
The arena became quiet for a extremely emotional homage before the fight as ten bells tolled in memory of the city's native Hatton, who succumbed 46 years old in September.
It was the first major televised boxing event in the city since Hatton's death. As the final chime disappeared, the silence transitioned to a roar of "there's only one Ricky Hatton".
The fighting inside the ropes equaled the sentiment. The eventual winner was sent to the canvas by a significant blow flush on the face in the second round, rising shakily to his position on the referee's count.
But the traditional red equipment of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was injured early, significant bruising developing under his eye as the duo exchanged punishing blows.
The challenger, 27, connected with strong blows but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor narrowly won the decision with judges scorecards of draw, narrow lead and clearer margin, but the two athletes were determined and courageous, everything their idol the legend embodied.
