Inca Garcilaso de la Vega in 1617 wrote "Comentarios Reales de los Incas" which is a history of the incans collected from oral tales.

In that he said that Tupac Inca Yupanqui and his general Sinchiruca conquered northern chile down to the Maule River (about half the modern country) with an army of 50,00 men in the 1470s but were unable to cross the maule due to fierce resistance from the southern chile mapuche tribes.

So northern chile was conquered by the incas. When Pizarro in turn conquered them in his peruvian campaign one of the men with him, Diego de Almagro, went south in 1536 to take stock of the southern part of their new realm. de Almagro took the 'Inca Trail' from Machu Picchu which went over the Bolivian Altiplano and led the first spanish troops into Chike. He went as far south as Linares Province where spanish troops fought the mapuche themselves for the first time.

de Almagro returned to peru, fought a series of battles against Pizarro and was executed for treason. Pizarro then sent one of his more loyal men down to retake control of chile. That being Pedro de Valdivia who crossed the Atacama Desert rather than taking the 'Inca Trail'. And de Valdivia was the real spanish conquerer of chile, he founded Santiago, fought a bunch of battles with the indians and became the first royal governor of chile.

Neither however were the first europeans to reach modern chile. Magellen landed on the southern coast during his circumnavigation of the world.