What is the ruling on the prayer of someone who intended that the rak'ah (unit of prayer) in which he joined as a latecomer was his first, then became confused and delayed completing the intention?

When a latecomer (masbuq) intends to join the prayer, he must specify the particular prayer he intends to perform, such as Dhuhr or Asr. Some scholars hold that intending the obligatory prayer of the time is sufficient. This intention should be concurrent with the takbirat al-ihram (definition) (the opening takbir) or immediately preceding it. The worshipper is not required to intend anything beyond this, nor to intend the first or second rak'ah, because the intention for the prayer encompasses all its parts. Likewise, one must abandon obsessions and turn away from them.