If I submit my 2018 medical expenses to my HSA in 2019, should I deduct them from my 2018 or 2019 taxes?

I have not submitted my medical expenses to my HSA account for reimbursement for my 2018 medical expenses.  I plan to submit them later in 2019.  I expect that I will then receive a 1099-SA for 2019 showing the HSA distributions.  Will these distributions be subtracted from my 2019 itemized medical deductions on my 2019 taxes?  In which case for 2018, I should include the full amount of my medical expenses for my itemized medical deductions and not subtract the HSA distributions that I have not yet submitted?  Is that correct?  Or should I subtract them for my 2018 itemized medical deductions on my taxes.  I am taking itemized deductions this year.