British light-heavyweight Joshua Buatsi made a winning yet unimpressive start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round bout at the Manchester venue.
But the challenger found success, landing some telling individual punches in a fight where the techniques never quite clicked, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best showing but what defines champions? They prevail," Buatsi said in the ringside as he was faced negative reactions from the spectators.
The Londoner bounced back after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Various analysts felt the challenger, 31, deserved the victory but the Derbyshire fighter suffered the second defeat of his 28-match career.
The Champion Earns Win in Uneventful Affair
The fighter's advancement has plateaued in the past few years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to realize his potential - possibly in what feels like a last chance - under fresh management.
He opened tentatively, with both competitors ready to overcommit in a cagey initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second fight at light-heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for the favorite, who utilized a solid defense to edge the more effective stanzas.
The crowd's patience diminished because of regular grabbing, with the challenger falling to the floor various instances during clinches.
The underdog ended stronger, but many rounds were challenging to assess. However, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor moves on, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Hatton Memorial Inspires All-Manchester Contest
In the supporting bout, Arthur beat Bradley Rea by divided decision in a outstanding local rivalry battle to win the European light heavyweight belt.
The stadium grew hushed for a extremely emotional memorial prior to the bout as 10 bells tolled in honor of Manchester's own Ricky Hatton, who passed away at age 46 in recently.
It was the premier televised match card in the location since Hatton's death. As the concluding sound disappeared, the silence transitioned to a roar of "only one Hatton".
The fighting inside the ropes reflected the sentiment. The eventual winner was floored by a left hook squarely on the jaw in the initial stage, rising shakily to his position on the referee's count.
But the traditional red shorts of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was damaged early, heavy swelling developing under his eye as the pair landed hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the pace rarely dropped over twelve rounds.
The victor barely secured the verdict with scoring tallies of 114-114, narrow lead and wider gap, but both fighters were relentless and courageous, exactly what their hero Hatton represented.
