British light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a competitive ten-round contest at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a contest where the styles failed to mesh, with frequent clinching spoiling the action.
Two judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my best display but how do champions respond? They win," the victor said in the arena as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, deserved the decision but the British boxer suffered the second loss of his 28-fight career.
Buatsi Secures Win in Dull Affair
Buatsi's progress has slowed in recent years through contract problems and extended periods of lack of fights.
Earlier forecast as the future of UK boxing, he now stands trying to achieve expectations - possibly in what seems like a ultimate opportunity - under fresh management.
He started carefully, with neither fighter willing to take risks in a tentative early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was making just his second appearance at light-heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who operated with a solid defense to barely take the more effective rounds.
The crowd's patience decreased during frequent holding, with the challenger slipping to the canvas several times during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter Benavidez, and Russian star Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Fight
In the secondary fight, Arthur beat Bradley Rea by divided decision in a terrific all-Manchester fight to secure the continental title.
The arena became quiet for a extremely emotional memorial prior to the bout as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the first major televised boxing event in the urban center since Hatton's passing. As the concluding sound faded, the quiet transitioned to a roar of "there's only one Hatton".
The action inside the ropes matched the sentiment. The eventual winner was knocked down by a significant blow squarely on the face in the early round, getting up unsteadily to his feet on the eight count.
But the red-colored attire of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was damaged soon, significant bruising developing under his eye as the fighters landed punishing blows.
The challenger, twenty-seven, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the intensity hardly diminished over twelve rounds.
The victor edged the result with official scores of even score, 115-113 and clearer margin, but both fighters were persistent and brave, everything their hero Hatton stood for.
