From the Classic Boxing Society YouTube page...

HENRY ARMSTRONG VS. FRITZIE ZIVIC II - JAN 17th 1941 - Original Radio Broadcast with updated audio preview...

"A great fighter went over the fistic horizon last night in Madison Square Garden. Henry Armstrong, the gallant, tornadic Hammering Hank of another day whose little fists pounded him to the distinction of being the ring's only exponent to hold three titles at the same time, was knocked out in 12 rounds of savage fighting....
"The end came after 52 seconds of the 12th round.... Referee Arthur Donovan mercifully ended the battle after twice having entreated the gallant Armstrong to retire, only to have his pleas rejected. Once, after the tenth round, Donovan solemnly notified Armstrong that he would give him on more round. Armstrong retorted to the warning with a flash of the fighting demon of old. It was as if he wanted to demonstrate that, though battered and bruised, cut and bleeding, his eyes puffed and cut, he still had plenty of fight left.
"Through the 11th round he pulled the crowd to its feet in as glorious a rally as this observer has seen in 25 years of attendances at these ring battles. The former champion hammered Zivic all over the ring. He pelted the title-holder with lefts and rights to the body, plied him with savage thrusts of the left and wicked right smashes to the face and head. Repeatedly Armstrong grazed the jaw with desperate rights, blows with which he hoped to turn the tide of crushing defeat that was engulfing him. For two minutes Armstrong went beserk. He was a fighting maniac in the one flash he gave of the Hammering Henry of old.
"It was glorious, spectacular while it lasted. Zivic was too busy trying to defend himself in this unlooked-for charge to launch a counterfire. But then Zivic stepped to the attack and through the last minute of the 11th round he hammered and punched Armstrong mercilessly with short, choppy but stinging lefts and rights that ripped open old wounds and started a flow of blood.
[Examined by the doctor between rounds Armstrong was allowed to continue and he] "started the 12th as if to press his dynamic recovery. But he had given all his strength in that 11th round stand. Hammering Henry shuffled into a barrage of straight lefts, a criss-cross fire of lefts and rights, punishing, cutting blows. He tried a roundhouse right for the jaw, missed and slipped. Up he came, facing his foe, charging recklessly, only to be pelted by Zivic's shower of blows. When Donovan realized what Armstrong must have known but would not admit, the referee stepped between the fighters and waved an end to the battle, and Armstrong's career."

(James P. Douglas, New York Times)