British light-heavyweight Joshua Buatsi made a winning yet disappointing start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a tight 10-round bout at the boxing arena.
But the challenger landed significant shots, delivering effective clean blows in a contest where the approaches never quite clicked, with constant grabbing spoiling the action.
The officials judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They succeed," Buatsi stated in the arena as he was greeted with boos from the audience.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts felt Parker, 31, should have been awarded the decision but the Derbyshire fighter suffered the second defeat of his 28-fight career.
The Champion Claims Win in Uneventful Affair
The fighter's advancement has stalled in recent years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter ready to be aggressive in a tentative initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand in the contest, was making just his second bout at light-heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for Buatsi, who operated with a protective stance to edge the better periods.
The spectators' acceptance diminished during frequent holding, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog finished the stronger, but multiple periods were difficult to score. However, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Homage Inspires All-Manchester Contest
In the supporting bout, Lyndon Arthur defeated Rea by split-decision in a outstanding local rivalry fight to win the European light-heavyweight belt.
The stadium became quiet for a extremely emotional homage ahead of the contest as ten bells rang in memory of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the premier televised fight night in the location since Hatton's death. As the concluding sound disappeared, the quiet transitioned to a roar of "there's just one Hatton".
The fighting during the bout reflected the emotion. Arthur was floored by a powerful punch squarely on the jaw in the early round, getting up unsteadily to his feet on the eight count.
But the red-colored attire of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was damaged early, significant bruising forming under his orbital area as the duo landed powerful shots.
Rea, twenty-seven, landed power punches but the champion, 34, fought fire with fire with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur barely secured the decision with judges scorecards of draw, 115-113 and clearer margin, but each competitor were persistent and courageous, exactly what their idol Hatton stood for.
