UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a competitive ten-round bout at the boxing arena.
But Parker found success, landing some telling clean blows in a contest where the techniques never quite clicked, with excessive holding marring the fight.
Two judges had it 96-94 in favor to the winner, with the third a even score.
"It wasn't my finest display but what defines champions? They prevail," the victor commented in the ring as he was met by disapproval from the crowd.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts thought the challenger, 31, should have been awarded the win but the contender experienced the second defeat of his 28-bout professional journey.
The Champion Secures Victory in Dull Encounter
His career development has slowed in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors ready to be aggressive in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who operated with a tight guard to narrowly win the cleaner periods.
The crowd's patience wore thin during regular grabbing, with Parker going down several times during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Hatton Homage Motivates All-Manchester Fight
In the co-main event, Lyndon Arthur beat Rea by split-decision in a excellent local rivalry battle to secure the European light heavyweight title.
The arena grew hushed for a profoundly moving memorial prior to the bout as 10 bells tolled in remembrance of local hero Ricky Hatton, who succumbed aged 46 in September.
It was the premier televised boxing event in the city since the passing of Hatton. As the final chime disappeared, the stillness gave way to a chant of "only one Ricky Hatton".
The action during the bout matched the sentiment. The eventual winner was floored by a powerful punch flush on the jaw in the second round, standing uncertainly to his footing on the eight count.
But the Manchester United-red attire of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was damaged soon, significant bruising appearing under his orbital area as the fighters exchanged hard punches.
Rea, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the action hardly diminished over twelve rounds.
The victor edged the decision with official scores of 114-114, close margin and clearer margin, but each competitor were determined and brave, all the qualities their hero Hatton embodied.
