UK light heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a majority decision in a close 10-round fight at the boxing arena.
But Parker had his moments, delivering effective individual punches in a contest where the techniques didn't complement each other, with constant grabbing disrupting the action.
The officials judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my best performance but how do champions respond? They win," Buatsi said in the ringside as he was met by boos from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts thought the challenger, thirty-one, deserved the decision but the contender suffered the second setback of his 28-match career.
The Champion Earns Win in Slow Match
Buatsi's progress has plateaued in recent times through management issues and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now stands trying to achieve expectations - maybe in what feels like a last chance - under fresh management.
He opened tentatively, with neither fighter ready to take risks in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was making just his second fight at the higher weight class.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who operated with a protective stance to narrowly win the more effective rounds.
The crowd's patience wore thin during constant clinching, with the challenger going down various instances during grappling.
The underdog closed well, but multiple periods were hard to judge. Although, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the likes of hard hitter Benavidez, and Russian champion Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Homage Motivates All-Manchester Battle
In the co-main event, Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry fight to secure the European light heavyweight belt.
The stadium became quiet for a extremely emotional homage before the fight as 10 bells rang in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in last month.
It was the premier televised fight night in the city since the passing of Hatton. As the concluding sound faded, the silence became a chant of "there's just one Hatton".
The action inside the ropes matched the emotion. The eventual winner was floored by a significant blow squarely on the face in the early round, standing uncertainly to his footing on the count of eight.
But the traditional red equipment of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was damaged soon, noticeable damage appearing under his eye as the fighters traded hard punches.
Rea, 27, delivered effective strikes but Arthur, 34, matched the intensity with stinging uppercuts as the action rarely dropped over 12 rounds.
The victor edged the verdict with judges scorecards of draw, close margin and 115-112, but each competitor were relentless and full of heart, everything their inspiration the legend stood for.
