UK light heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a tight ten-round contest at the Manchester venue.
But Parker found success, landing some telling individual punches in a match where the approaches didn't complement each other, with frequent clinching spoiling the contest.
The scoring judges scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but what do champions do? They prevail," the victor commented in the arena as he was met by disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers thought the challenger, 31, should have been awarded the victory but the British boxer endured the second loss of his 28-match professional journey.
Buatsi Secures Triumph in Dull Affair
His career development has stalled in recent years through promotional disputes and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - possibly in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers willing to take risks in a tentative early stages.
The challenger, 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 fight at light heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who operated with a protective stance to barely take the cleaner periods.
The crowd's patience wore thin during regular grabbing, with the challenger falling to the floor multiple occasions during close exchanges.
Parker ended stronger, but many rounds were challenging to assess. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi progresses, but with the caliber of hard hitter David Benavidez, and Russian champion Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Homage Motivates All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to secure the European light-heavyweight title.
The arena became quiet for a extremely emotional memorial prior to the bout as 10 bells sounded in memory of Manchester's own Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised boxing event in the urban center since Hatton's death. As the concluding sound disappeared, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The competition within the ring equaled the feeling. Arthur was knocked down by a significant blow squarely on the face in the initial stage, standing uncertainly to his feet on the count of eight.
But the red-colored shorts of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was damaged soon, heavy swelling forming under his eye as the fighters landed punishing blows.
Rea, 27, landed power punches but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity seldom decreased over twelve rounds.
Arthur barely secured the decision with official scores of even score, narrow lead and wider gap, but each competitor were persistent and courageous, all the qualities their idol Hatton stood for.
