The seven-time Wimbledon champion beat her Spanish foe 6-2, 6-2 in the 1:04 match at the All-England Club in London. Riske upset No. 1 Ashleigh Barty to reach her first Grand Slam quarterfinal. She'll face Williams Tuesday in London.
"Every match is still super hard. Today I won a lot of points," Williams told reporters. "It wasn't your average 6-2, 6-2 score. There weren't too many 40-love games at all.
"I think everyone is also getting better and as the tournament goes on that's when the better players are surviving."
Williams won Monday's first set in 31 minutes. She fired 21 winners against Suarez Navarro's nine winners. The 23-time Grand Slam champion lost in the third round of the French Open last month. She pulled out of the Italian Open due to a knee injury. Williams said she feels healthier and is working off the rust.
"It's definitely a lot of both," Williams told reporters. "The rust is definitely wearing off. Most of all I feel confident that I can actually move and I don't have to go for winners so soon because I'm in pain.
"It's like 'oh, now I can just play my game and hit shots and not have to worry about anything else.' It's good when your mind is clear and you can just play."
Williams said Riske is a great person and a "fighter on the court."
"She is playing really great, especially on the grass," Williams said. "She is attacking that ball really well. She doesn't let anything limit her."