Young claimed a 6-1, 6-7 (0-7), 7-5 victory over the fourth-seeded Garcia-Lopez in a match that took move the 2 1/2 hours. Garcia-Lopez fired nine aces and didn't commit a double fault but had his serve broken five times, including twice in the third set.
No. 1-seeded Andy Murray had little trouble dispatching Michael Berrer 6-4, 6-2. Their match took just 70 minutes with Murray winning 75 percent of the points on serve saving both break points created by Berrer.
Gail Monfils, the No. 2 seed, needed a third set to advance to the quarterfinals. He defeated Santiago Giraldo 6-4, 4-6, 6-1. Monfils lost two points over his three third-set service games.
Qualifier Go Soeda beat Tobias Kamke 6-2, 7-6 (9-7) and Grigor Dimitrov took a 7-6 (10-8), 6-1 decision from Simone Bolelli in Thursday's other matches.
Friday's quarterfinals schedule calls for Murray to take on Dimitrov and third-seeded Gilles Simon to battle Matthias Bachinger in the top half of the bracket. The other matches are Soeda versus Young and Monfils against Jarkko Nieminen.
The Thailand Open title, to be decided Sunday, is worth $107,000.