British light heavyweight Joshua Buatsi earned a win yet disappointing beginning to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a close 10-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful individual punches in a contest where the techniques never quite clicked, with frequent clinching marring the fight.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best showing but what do champions do? They win," the victor commented in the arena as he was faced boos from the crowd.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts thought Parker, 31, should have been awarded the decision but the Derbyshire fighter experienced the second setback of his 28-fight career.
The Champion Earns Triumph in Uneventful Match
Buatsi's progress has plateaued in recent times through contract problems and long spells of lack of fights.
Previously predicted as the future of the British fight scene, he now stands trying to realize his potential - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors willing to overcommit in a cagey initial rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who utilized a tight guard to narrowly win the better stanzas.
The crowd's patience diminished during constant clinching, with Parker falling to the floor several times during close exchanges.
Parker finished the stronger, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester battle to win the European light heavyweight championship.
The arena fell silent for a extremely emotional memorial prior to the bout as 10 bells rang in memory of Manchester's own Ricky Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the concluding sound faded, the stillness became a roar of "there's just one Hatton".
The fighting during the bout reflected the emotion. Arthur was knocked down by a left hook directly to the chin in the second round, rising shakily to his feet on the count of eight.
But the red-colored equipment of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was marked up soon, noticeable damage developing under his face as the pair exchanged hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the action rarely dropped over twelve rounds.
Arthur narrowly won the decision with scoring tallies of draw, close margin and wider gap, but each competitor were relentless and brave, exactly what their inspiration the legend embodied.
