Top-seeded Feliciano Lopez capitalized on Sam Groth's frequently errant serving Wednesday night to easily advance 6-3, 6-3 into the quarterfinals of the U.S. Men's Clay Court Championships.

The 34-year-old Spaniard, who's at a career high No. 12 in the ATP World Tour rankings, broke Groth three times. Although the powerful Australian belted nine aces, he missed half his first serves, never giving himself a chance to hang in against Lopez's vastly superior baseline attack.

"You feel he has the fastest serve (on the ATP World Tour), for sure," Lopez said. "But he gave me a couple of double faults early and I got the break to get on top of him. I was very focused on trying to read his serve. I got a lot of balls back. I was really happy I was able to return quite good tonight."

In an earlier match between two Americans from Southern California, eighth seed Sam Querrey broke open a tight match by winning 24 of 30 points in the third set to advance 6-1, 4-6, 6-0 over Steve Johnson. Querrey said the two of them first played when Querrey was 11, conceding it's difficult to go against a close friend.

"Sure, I'm glad I won," Querrey said, "but it doesn't feel the same as beating one of the European guys."

South African Kevin Anderson similarly dispatched Ricardas Berankis of Lithuania 6-7 (4), 6-0, 6-3. France's Jeremy Chardy, the seventh seed, eliminated Dusan Lajovic of Serbia 6-3, 6-3.

Four quarterfinal spots remain to be filled for North America's only men's clay court tournament.