UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to life under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a close 10-round contest at the boxing arena.
But Parker landed significant shots, landing some telling individual punches in a match where the approaches failed to mesh, with frequent clinching disrupting the contest.
The scoring judges judged it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my finest performance but what defines champions? They win," Buatsi stated in the ring as he was faced disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts believed the challenger, 31, should have been awarded the victory but the British boxer suffered the second setback of his 28-match career.
The Champion Earns Victory in Slow Match
Buatsi's progress has stalled in recent years through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of British boxing, he now stands trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under fresh management.
He started carefully, with both competitors willing to take risks in a tentative opening few rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after damaging his hand in the contest, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who utilized a tight guard to barely take the more effective rounds.
The crowd's patience wore thin amid regular grabbing, with the challenger slipping to the canvas various instances during grappling.
Parker closed well, but several stanzas were hard to judge. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Memorial Fuels Local Rivalry Fight
In the supporting bout, Arthur beat Bradley Rea by divided decision in a outstanding Manchester vs Manchester contest to secure the continental championship.
The stadium became quiet for a extremely emotional tribute before the fight as a bell ceremony tolled in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in last month.
It was the premier televised match card in the city since Hatton's passing. As the concluding sound faded, the stillness transitioned to a shout of "only one Hatton".
The competition within the ring matched the feeling. The eventual winner was knocked down by a left hook directly to the chin in the initial stage, getting up unsteadily to his footing on the eight count.
But the red-colored attire of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged soon, heavy swelling developing under his eye as the duo exchanged powerful shots.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the intensity seldom decreased over twelve rounds.
Arthur barely secured the verdict with official scores of even score, narrow lead and clearer margin, but each competitor were persistent and full of heart, exactly what their hero Hatton stood for.
