UK light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a competitive ten-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful clean blows in a contest where the styles failed to mesh, with excessive holding spoiling the fight.
Two judges scored it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my finest showing but what do champions do? They win," Buatsi commented in the ring as he was met by disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to claim a 20th career victory.
Several boxing experts felt Parker, thirty-one, deserved the win but the contender endured the second setback of his 28-match career.
Buatsi Claims Victory in Dull Encounter
Buatsi's progress has plateaued in recent years through contract problems and extended periods of lack of fights.
Previously predicted as the future of British boxing, he now is positioned trying to achieve expectations - possibly in what seems like a final roll of the dice - under recent support.
He began cautiously, with the two boxers prepared to overcommit in a calculated opening few rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was participating in his second fight at the higher weight class.
By the fight's midpoint, Parker had kept it close, causing problems for Buatsi, who utilized a solid defense to narrowly win the more effective rounds.
The spectators' acceptance diminished during regular grabbing, with Parker slipping to the canvas various instances during close exchanges.
Parker closed well, but multiple periods were hard to judge. However, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor advances, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a terrific local rivalry battle to capture the European light heavyweight belt.
The arena fell silent for a profoundly moving memorial prior to the bout as a bell ceremony rang in remembrance of the city's native Hatton, who succumbed aged 46 in September.
It was the first major televised fight night in the urban center since Hatton's death. As the final chime ended, the quiet transitioned to a roar of "only one Ricky Hatton".
The fighting during the bout equaled the emotion. Arthur was sent to the canvas by a powerful punch flush on the face in the initial stage, rising shakily to his feet on the referee's count.
But the red-colored equipment of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was marked up early, noticeable damage forming under his eye as the pair exchanged hard punches.
Rea, 27, landed power punches but Arthur, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over the full distance.
Arthur barely secured the decision with official scores of 114-114, close margin and 115-112, but the two athletes were persistent and courageous, all the qualities their hero the legend stood for.
