UK light heavyweight Joshua Buatsi made a winning yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close ten-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful single shots in a match where the approaches didn't complement each other, with constant grabbing marring the action.
Two judges judged it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my best performance but what do champions do? They succeed," the victor said in the ringside as he was met by disapproval from the crowd.
The Londoner bounced back after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th career victory.
Some ringside observers thought the challenger, 31, merited the victory but the British boxer endured the second setback of his 28-fight professional journey.
The Champion Claims Victory in Slow Encounter
The fighter's advancement has plateaued in recent years through promotional disputes and long spells of lack of fights.
Once tipped as the future of UK boxing, he now finds himself trying to realize his potential - perhaps in what feels like a last chance - under new promotional backing.
He began cautiously, with both competitors willing to be aggressive in a tentative initial rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was competing in only his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who operated with a solid defense to edge the more effective rounds.
The audience's tolerance wore thin because of frequent holding, with Parker going down several times during clinches.
Parker finished the stronger, but many rounds were challenging to assess. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Motivates All-Manchester Contest
In the secondary fight, Arthur overcame Rea by divided decision in a terrific local rivalry fight to win the European light-heavyweight belt.
The stadium grew hushed for a profoundly moving homage before the fight as ten bells tolled in remembrance of local hero Hatton, who died aged 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the concluding sound ended, the silence gave way to a chant of "there's only one Hatton".
The action within the ring reflected the feeling. Arthur was floored by a significant blow directly to the jaw in the early round, rising shakily to his feet on the referee's count.
But the red-colored shorts of the fighter soon came forward again. On the opposite side, Rea - in opposing blue - was marked up quickly, heavy swelling appearing under his orbital area as the fighters exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the action seldom decreased over twelve rounds.
Arthur narrowly won the result with scoring tallies of even score, 115-113 and clearer margin, but both fighters were relentless and brave, everything their inspiration the legend represented.
