Spain squad for Chile friendly
Attacking midfielder Mata, 20, is a product of the Real Madrid youth team while 23-year-old Llorente is a tall and aggressive centre-forward with a powerful shot. Both are in the squad for the first time.
"The national side must evolve according to its needs," Del Bosque told a news conference on Friday. "We cannot close ourselves off from changing things at a certain point."
The former Real Madrid coach said he had brought Llorente in partly because of the delicate state of strikers Fernando Torres and Daniel Guiza, who are both just back from injury.
"We will not force anyone to play a match if they are not fully fit," Del Bosque said.
The European Champions are undefeated in 27 matches stretching back to November 2006, when they lost 1-0 to Romania in a friendly in Cadiz.
They lead their qualifying group for the 2010 World Cup in South Africa with four wins from four matches.
Del Bosque was forced to leave Andres Iniesta out of the squad for Wednesday's match in Villarreal. The Barcelona midfielder injured a thigh in the Champions League draw with Basel this month and is out for six to eight weeks.
Spain have played Chile six times, winning five and drawing one.
Goalkeepers: Iker Casillas (Real Madrid), Pepe Reina (Liverpool).
Defenders: Raul Albiol (Valencia), Alvaro Arbeloa (Liverpool), Joan Capdevila (Villarreal), Juanito (Real Betis), Carlos Marchena (Valencia), Carles Puyol (Barcelona), Sergio Ramos (Real Madrid).
Midfielders: Xabi Alonso (Liverpool), Santi Cazorla (Villarreal), Cesc Fabregas (Arsenal), Xavi (Barcelona), Juan Mata (Valencia), Albert Riera (Liverpool), Marcos Senna (Villarreal).
Forwards: David Villa (Valencia), Daniel Guiza (Fenerbahce), Fernando Torres (Liverpool), Fernando Llorente (Athletic Bilbao).