British light-heavyweight Joshua Buatsi made a winning yet underwhelming beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a tight 10-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful individual punches in a fight where the approaches didn't complement each other, with constant grabbing disrupting the contest.
Two judges judged it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi stated in the ringside as he was met by boos from the audience.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in February - to earn a 20th career victory.
Several boxing experts thought Parker, 31, merited the victory but the Derbyshire fighter suffered the second defeat of his 28-fight professional journey.
The Champion Secures Triumph in Uneventful Encounter
Buatsi's progress has stalled in recent times through contract problems and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under fresh management.
He started carefully, with neither fighter ready to be aggressive in a cagey initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to edge the more effective stanzas.
The crowd's patience diminished amid frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
Parker closed well, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Memorial Inspires Local Rivalry Battle
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a terrific local rivalry contest to win the European light-heavyweight championship.
The stadium fell silent for a deeply poignant homage before the fight as 10 bells rang in honor of local hero Ricky Hatton, who died 46 years old in last month.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the last bell disappeared, the stillness became a shout of "there's only one Ricky Hatton".
The fighting during the bout reflected the feeling. The eventual winner was floored by a left hook squarely on the face in the second round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured early, significant bruising developing under his face as the fighters exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with effective uppercuts as the action hardly diminished over 12 rounds.
The victor edged the verdict with judges scorecards of 114-114, 115-113 and wider gap, but both fighters were determined and courageous, exactly what their inspiration Hatton represented.
