British light-heavyweight Joshua Buatsi made a winning yet underwhelming debut to life under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a tight 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling clean blows in a fight where the approaches failed to mesh, with excessive holding disrupting the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi commented in the ringside as he was greeted with negative reactions from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in February - to secure a 20th career victory.
Several boxing experts believed the challenger, thirty-one, merited the decision but the British boxer endured the second setback of his 28-match career.
Buatsi Earns Triumph in Dull Encounter
His career development has stalled in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the next star of UK boxing, he now finds himself trying to achieve expectations - perhaps in what feels like a last chance - under recent support.
He started carefully, with neither fighter willing to be aggressive in a calculated opening few rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was competing in only his second fight at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who utilized a protective stance to edge the better rounds.
The audience's tolerance diminished amid constant clinching, with Parker slipping to the canvas various instances during clinches.
The underdog closed well, but several stanzas were challenging to assess. Although, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the supporting bout, Arthur defeated Rea by divided decision in a excellent local rivalry battle to capture the European light-heavyweight belt.
The stadium grew hushed for a extremely emotional homage prior to the bout as ten bells tolled in memory of Manchester's own Ricky Hatton, who died 46 years old in September.
It was the premier televised fight night in the city since the passing of Hatton. As the last bell faded, the silence became a roar of "there's just one Ricky Hatton".
The fighting within the ring equaled the emotion. Arthur was knocked down by a significant blow squarely on the chin in the initial stage, standing uncertainly to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged early, noticeable damage appearing under his eye as the pair traded hard punches.
Rea, 27, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the action hardly diminished over the full distance.
Arthur barely secured the result with scoring tallies of 114-114, close margin and clearer margin, but each competitor were persistent and brave, exactly what their inspiration Hatton represented.
