Kei Nishikori, seeded fifth, ousted Cilic 6-4, 6-2 and will now meet Marinko Matosevic in the semifinals.
Matosevic fought off No. 7 seed Alexandr Dolgopolov 6-7 (6-8), 6-2, 6-4.
Lopez defeated Sock 6-4, 6-3 to close out what had been a big week for the 20-year-old American.
Sock had played in only one ATP match this year and lost that one before defeating No. 2 seed Milos Raonic and James Blake in this event. Sock had an unbeaten, 80-match career as a high school player in Kansas and should make a big move up the world rankings next week from his current position of No. 168.