Such has been his form since falling as low as world number eight in March that the 33-year-old could end the season top of the rankings.
"It was a very easy match. He couldn't do anything on my serve. He was struggling with the return," Federer told reporters.
"I'm happy I had a quick match, because I have a lot of matches in the coming weeks. Gilles' game completely fell apart and his level dropped. It was a great first round for me."
Nadal, playing through appendicitis, was equally impressive, needing just 57 minutes to dispatch France's Herbert.
The former world number one, who could miss the season-ending ATP World Tour Finals next month depending on surgery, broke his opponent's serve five times in a second seamless victory in three days.
"I'm still very tired during the matches," Nadal told a press conference. "But physically I'm improving. I feel much better than a few days ago.
"I'm surprised that I advanced that easy to the quarter-finals. I didn't expect that before the tournament."
(Writing by Tom Hayward, editing by Stephen Wood)
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