British light-heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a tight 10-round fight at the Manchester venue.
But the challenger found success, delivering effective single shots in a match where the techniques failed to mesh, with constant grabbing spoiling the action.
The officials had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best performance but what do champions do? They win," the victor said in the ring as he was faced disapproval from the audience.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in February - to earn a 20th career victory.
Some ringside observers felt the challenger, 31, merited the win but the contender experienced the second setback of his 28-bout professional journey.
The Champion Secures Triumph in Slow Affair
His career development has slowed in recent times through promotional disputes and long spells of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to realize his potential - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers prepared to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who operated with a solid defense to edge the more effective rounds.
The crowd's patience decreased amid regular grabbing, with the challenger slipping to the canvas various instances during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Inspires Local Rivalry Contest
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a excellent local rivalry battle to capture the continental title.
The venue grew hushed for a profoundly moving tribute ahead of the contest as ten bells sounded in honor of the city's native Ricky Hatton, who succumbed aged 46 in September.
It was the premier televised fight night in the city since the passing of Hatton. As the last bell ended, the silence became a shout of "there's only one Ricky Hatton".
The competition inside the ropes equaled the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the chin in the initial stage, getting up unsteadily to his position on the eight count.
But the traditional red shorts of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was marked up soon, noticeable damage developing under his orbital area as the pair exchanged powerful shots.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the action rarely dropped over 12 rounds.
The victor edged the decision with scoring tallies of draw, close margin and 115-112, but both fighters were persistent and full of heart, exactly what their inspiration the legend stood for.
