UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a close 10-round bout at the boxing arena.
But the challenger found success, landing some telling single shots in a contest where the approaches didn't complement each other, with constant grabbing marring the fight.
The scoring judges had it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi said in the ring as he was faced boos from the spectators.
The Londoner got back to winning after his initial pro loss - an epic battle with his previous opponent in February - to secure a twentieth professional win.
Some ringside observers believed Parker, thirty-one, should have been awarded the decision but the contender endured the second setback of his 28-fight career.
Buatsi Claims Victory in Slow Match
Buatsi's progress has slowed in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the next star of British boxing, he now stands trying to achieve expectations - maybe in what appears to be a last chance - under fresh management.
He started carefully, with the two boxers prepared to take risks in a cagey early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a solid defense to narrowly win the better stanzas.
The spectators' acceptance diminished amid frequent holding, with Parker going down various instances during clinches.
Parker closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian champion Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Memorial Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur defeated Bradley Rea by split-decision in a excellent local rivalry fight to capture the continental belt.
The arena became quiet for a extremely emotional memorial before the fight as ten bells sounded in memory of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the premier televised fight night in the location since the passing of Hatton. As the final chime disappeared, the stillness became a chant of "there's only one Ricky Hatton".
The fighting inside the ropes matched the sentiment. The eventual winner was floored by a powerful punch squarely on the face in the early round, standing uncertainly to his feet on the count of eight.
But the red-colored attire of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was marked up early, significant bruising appearing under his face as the fighters landed punishing blows.
The challenger, 27, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over twelve rounds.
The victor edged the decision with judges scorecards of draw, close margin and clearer margin, but each competitor were persistent and courageous, all the qualities their idol Hatton stood for.
