The San Francisco 49ers' decision to replace Alex Smith with Colin Kaepernick at quarterback was not planned.

"It was not a pre-determined move," Jim Harbaugh said. "The decision was made, when Alex got hurt, Colin played, played well in his first start. Came back the next week, still felt that against New Orleans that Colin gave us the best chance to win. He was healthier and played well.

"Then after that, (we) saw enough really good things that we wanted to have the same faith and trust in Colin that we'd show in Alex. And it's pretty well documented how we felt about both guys."

Kaepernick is preparing for his first playoff start with the Green Bay Packers visiting the 49ers on Saturday.

"His understanding of it this early in the week is savant-like," Harbaugh said of Kaepernick's grasp of the 49ers' game plan.