Too late to edit my own comment but technically it is incorrect. If you keep meticulous records of the offsetting losses, the IRS may allow you to claim zero gambling income in that fiscal year and relieve you of having to pay tax on income.

What I stated above is true across fiscal years. If you win a $10,000 jackpot on December 31, and lose all $10,000 on January 1 (or at any point over the next 12 months), the above comment is true. You don't get to reduce your income in the next year by the $10,000 of losses, or edit the previous year's return, or offset the earlier win in any way.