‘Tank’ seemed sluggish and disinterested at times, fighting with his hands behind his back and taunting his opponent too much in spurts.
The 22 year-old eventually got the job done in the eight by hitting Fonseca behind the head before hitting the Costa Rican as he fell to his knees.
Other results:
Pre-fight favorite Badou Jack was ruthless from the off as the former super-middleweight title holder added a light-heavyweight version to his haul.
The US-based Swede piled pressure on Welshman Nathan Cleverly for the first four rounds before persuading Tony Weeks to step in and stop the fight in the fifth.
With the win, Jack picks up the WBA ‘regular’ version and immediately called out Adonis Stevenson for a unification.
Andrew Tabiti was in dominant form as the cruiserweight contender overcame his toughest test yet against former world champion Steve Cunningham.
Tabiti won virtually every round on the WBN live scorecard, which was almost matched by the ringside officials, who saw it 100-90 and 97-93 twice in favour of the TMT man.
In an entertaining welterweight contest, late replacement Yordenis Ugas shocked Thomas Dulorme over ten rounds.
Ugas, who was drafted in when former world champion Shawn Porter was ruled out, dropped Dulorme twice in the second before the Puerto Rican was deducted a point twice for low blows.
In the end, those incidents were telling as Ugas took a 94-91 and 93-92 (twice) triumph with the judges.
Money Team member Juan Heraldez picked himself up off the canvas and ploughed through some hairy moments to pick up a unanimous verdict against Jose Borrego.
In trouble at the end of the sixth and down late in the fight, Heraldez had done enought earlier in the first to preserve his unbeaten record on all three scorecards.
Californian Mark Hernandez ended Kevin Newman’s undefeated run after a six-round tussle at 168 pounds.
The 24 year-old was able to card a unanimous verdict and push his record to 10-1 following a first loss back in March.
British super-middleweight Savannah Marshall began her career with a comprehensive four-round victory over Sydney LeBlanc.
Judges scored all four rounds to the former GB Boxing member who made a winning start to her time with Mayweather Promotions.
