Note that it's possible that some nodes have the first transaction in their mempool and some have the second transaction, but no node would keep both transactions.
Now I get, that’s why both the transactions, the first one and second one both have almost same chance of been confirmed, since the node that holds the first transaction could still add it to the block it mines (if the fee later meets the node’s requirement), if he mines first before the other block and then it invalidates the second transaction