Yep w2 thanks for the correction. However, my interpretation of the law is that the diary alone will not suffice and will require further supporting documentation:


'It is important to keep an accurate diary or similar record of your gambling winnings and losses. To deduct your losses, you must be able to provide receipts, tickets, statements or other records that show the amount of both your winnings and losses. Refer to Publication 529, Miscellaneous Deductions, for more information.'

Note the second sentence here.