By Alastair Himmer
Nadal was stunned 2-6 7-6 6-3 by countryman Guillermo Garcia-Lopez in the Thailand Open semi-finals at the weekend and insisted he will not be so charitable in Tokyo.
"Tomorrow will be a difficult match," Nadal told reporters Monday. "It will be a very fast surface and Giraldo is a very dangerous player.
"There is not much you can do in a matter of days. If you look at the way I lost in Thailand you would say I have to make some changes. I need to be more aggressive."
World number 63 Santiago is not expected to pose a serious threat to Nadal, who has won three of this year's four grand slam tournaments, including his first U.S. Open last month.
"This was an incredible season for me," he said. "I've been playing well all year. I had a bit of a problem with my knee in Australia but when I won in Monte Carlo everything changed.
"I started to play really well and get some confidence. The U.S. Open was very important for my career but I'm going to keep trying to improve everyday. That is always my goal."
Nadal is making his first appearance in Japan this week.
"I'm excited to be here," said the nine-times grand slam winner. "Japan is one of the places you definitely want to know and hopefully I will be able to come back."
(Editing by John O'Brien)