Federer believes Nadal is playing better than he did in losing the Australian Open final to Novak Djokovic, who was upset earlier in the week.
Both came through their respective quarter final matches yesterday to ensure the semi final scrap, with Spaniard Nadal eventually making his way past Russian tournament 12th seed Karen Khachanov 7-6 (7-2), 7-6 (7-2) in an extremely close match, and Federer beat unseeded Pole Hubert Hurkacz.
Nadal leads the head-to-head record against Federer 23-15, though the Swiss great has won the past five meetings - including his victory in the 2017 Shanghai Masters final.
"The fans are maybe more excited about us playing than me as I've always got to be focused on my own game".
"When Rafa is healthy, especially in a place like here in Indian Wells where he feels comfortable, he's clearly very tough to play, " Federer said.
It was the first match between the pair and far from one-sided, as Hurkacz had two break points but could seize neither. At 37, he became the oldest player to win a tour-level title since Marty Riessen won at Lafayette, Louisiana, in 1979 at the same age. Trailing 3-2 in the second set, Hurkacz had a break point, but Federer closed the game with consecutive forehand winners and an ace. Federer netted back-to-back volleys to give Hurkacz hope and another break point.
Tennis icons Roger Federer and Rafael Nadal will play out the 39th episode of their legendary rivalry in California as they meet in the semi finals of the Indian Wells Masters on Saturday - their first meeting on court since 2017.