CARSON, Calif. — Gennady Golovkin won his 20th consecutive middleweight title defense with a second-round knockout of Vanes Martirosyan on Saturday night. Golovkin (38-0-1, 34 KOs) tied Bernard Hopkins’ record for middleweight title defenses by sending Martirosyan down at 1:53 of the second round. After being tagged with a strong three-punch combination from Martirosyan (36-4-1)...