Top seed Andre Agassi continued his comeback from a two-month injury lay-off with victory over Kevin Kim at the Mercedes-Benz Cup in Los Angeles. Agassi beat his fellow American 6-2 7-5 to set up a quarter-final meeting with Thailand's Paradorn Srichaphan.
Srichaphan booked his place in the last eight with a 6-1 6-4 win over American wild card Paul Goldstein.
It is only the second time the Thai player has won two matches in a row in his past 14 events.
In other matches, Robby Ginepri beat James Blake 6-3 7-6 (7-2) in an all-American clash and Luxembourg's Gilles Muller saw off American Zack Fleishman 6-3 7-5.