British light-heavyweight Joshua Buatsi made a winning yet disappointing start to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But Parker had his moments, landing some telling single shots in a contest where the styles didn't complement each other, with constant grabbing disrupting the contest.
The scoring judges had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but what defines champions? They succeed," the victor commented in the arena as he was met by negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts felt Parker, thirty-one, deserved the win but the Derbyshire fighter suffered the second loss of his 28-match career.
Buatsi Claims Triumph in Slow Match
The fighter's advancement has slowed in the past few years through contract problems and extended periods of lack of fights.
Once tipped as the rising talent of British boxing, he now is positioned trying to realize his potential - possibly in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with the two boxers prepared to take risks in a cagey initial rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second bout at light heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who operated with a tight guard to edge the cleaner rounds.
The audience's tolerance decreased because of frequent holding, with Parker falling to the floor several times during close exchanges.
Parker ended stronger, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
The victor progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Hatton Tribute Inspires Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific local rivalry fight to capture the European light-heavyweight belt.
The arena fell silent for a profoundly moving memorial before the fight as a bell ceremony tolled in memory of the city's native Hatton, who passed away 46 years old in September.
It was the premier televised match card in the location since Hatton's death. As the concluding sound disappeared, the silence became a roar of "there's only one Hatton".
The fighting inside the ropes reflected the emotion. Arthur was floored by a significant blow flush on the face in the initial stage, standing uncertainly to his footing on the referee's count.
But the red-colored equipment of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was injured soon, noticeable damage forming under his face as the fighters traded powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace hardly diminished over the full distance.
The victor edged the result with official scores of draw, 115-113 and wider gap, but both fighters were relentless and courageous, all the qualities their hero Hatton represented.
