Yates's strategy changes after the time trial stage 16, when he successfully defended his lead ahead of Tom Dumoulin (Sunweb). Ahead of three mountain stages, all ending with summit finishes, he leads with 56 seconds over Dumoulin.
Chris Froome (Sky) sits fourth overall at 56 seconds. Domenico Pozzovivo (Bahrain-Merida) is in third.
"It's not up to me to attack and be aggressive," Yates said.
"I will ride aggressively and try to be as defensive as possible. I have almost a minute's lead."
Yates aggressive riding saw him take the pink jersey on Mount Etna. With the famous jersey, he won three summit finish stage at Gran Sasso, Osimo and Sappada. The Sappada stage came thanks to an 18-kilometre solo attack on his Grand Tour rivals.
"I am getting closer to the end, and as the days tick down. I will be careful," Yates continued.
"I have to do nothing. I will watch Tom and any other GC guys. It will be difficult. I will be careful and I will ride defensively."
The 25-year-old Briton rode through the rain showers along the shores of Lake Iseo to finish the 17th stage, a sprint won by Elia Viviani (Quick-Step Floors).
Stage 18 rides through the Po Valley, into Piedmont and up the 13.9-kilometre climb to Prato Nevoso for its finish.
"Tomorrow is good for Dumoulin or Pozzovivo. It's a long, steady climb. It will be good for any of the pure climbers," Yates added.
"I am expecting a difficult day. Every day has been hard. I am expecting more of the same."
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