British light heavyweight Joshua Buatsi earned a win yet underwhelming debut to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive 10-round bout at the Co-op Live Arena.
But the challenger found success, landing some telling clean blows in a fight where the approaches never quite clicked, with excessive holding spoiling the contest.
The officials had it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best performance but how do champions respond? They win," the victor said in the ring as he was met by disapproval from the audience.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Various analysts felt the challenger, 31, deserved the win but the contender experienced the second loss of his 28-bout professional journey.
Buatsi Earns Win in Dull Encounter
His career development has plateaued in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under recent support.
He started carefully, with the two boxers willing to be aggressive in a cagey initial rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second fight at light heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for Buatsi, who operated with a protective stance to narrowly win the better rounds.
The spectators' acceptance decreased amid constant clinching, with Parker falling to the floor several times during grappling.
Parker closed well, but several stanzas were challenging to assess. Although, previous titleholder Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the presence of power puncher Benavidez, and Russian star Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Tribute Inspires All-Manchester Battle
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry contest to win the European light-heavyweight belt.
The arena grew hushed for a extremely emotional homage ahead of the contest as a bell ceremony rang in memory of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the first major televised boxing event in the urban center since Hatton's passing. As the concluding sound ended, the quiet became a chant of "there's only one Ricky Hatton".
The fighting inside the ropes matched the sentiment. Arthur was sent to the canvas by a powerful punch squarely on the chin in the initial stage, standing uncertainly to his feet on the eight count.
But the traditional red equipment of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was damaged soon, noticeable damage appearing under his eye as the duo landed powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor narrowly won the result with official scores of even score, narrow lead and 115-112, but the two athletes were determined and courageous, all the qualities their inspiration the legend embodied.
