The American, who holds the interim WBA belt to Adrien Broner’s full title, won every round and had Karass on the canvas before a flurry in the ninth had the referee scrambling to end it.
Now undefeated in 22 bout with 20 knockouts, Thurman is one of the better up and comers of the division and will be no doubt hoping for a future shootout with the winner of the main event.
WBC super-bantamweight champion Leo Santa Cruz retained his green belt via a unanimous decision, although was made to work for it by a game Cesar Seda.
The 25 year-old, who is now undefeated through 27 contests, dropped Seda in the fifth in what was one of few one-sided rounds – as the talented challenger kept the fight competitive throughout.
Of those close rounds, I leaned towards two-weight world title holder Santa Cruz’s better quality punches, although two of the three ringside officials obviously saw them different judging by the cards of 116-111 and 115-112.
The third’s score of 117-110 came close to mine as I has Santa Cruz a convincing winner 118-109, although the victor himself was far from happy with his performance on the night.
Earlier, Beibut Shumenov dropped Tamas Kovacs in all three rounds of their short contest at the Alamodome in Texas as the WBA light-heavyweight champion set up a possible unification with Bernard Hopkins.
With Hopkins sitting at ringside waving a Shumenov poster, the Kazakhstan fighter made short work of the undefeated Slovakian, who certainly had a deceptive 23-0 record heading into the fight.
Obviously out of his depth, Kovacs took count from Shumenov’s left hand and his right, before referee Rafael Ramos correctly ended his misery to push the chamoion’s record to 14-1 with a ninth stoppage.
Follow on Twitter @PhilDJay for tweets of upcoming news on WBN
