There are a few things wrong with your question.
First, slavery, human sacrifice, and cannibalism were practiced, commonly, before the Spanish Conquistadors arrived in the Americas. The Spanish did not bring the first slaves to the Americas. Slaves were already here, and had been here, for a long time.
Second, yes, the indigenous people made poor slaves because they died of European illness in great numbers, and they could, and often did, run away, because they knew the people and the languages.
So, yes, the Spaniards imported slaves, though the Portuguese brought in many more. Most of them went to Brazil, where they were worked to death, unlike the mainland British colonies, where most slaves were allowed to form families and raise children.
" the first African slaves"
And I'm sure that all over the Americas people with room temperature IQ's will be nodding with satisfaction that you picked that nit as if somehow I was unfamiliar with your pedantic grade school resume of Human Slavery In the New World, and that they actually cared about such details.