Fourth-seeded German Kohlschreiber upset second seed Feliciano Lopez of Spain 6-2 6-7(4) 6-4.
The duo was evenly-matched but Kohlschreiber threatened his opponent's serve more often, breaking him three times from 13 chances.
The world number 34 faced five break points from the 16th-ranked Lopez, but saved them all.
Third seed Cilic of Croatia beat Tommy Haas of Germany 6-3 6-4.
Giant 6'6" Cilic sent down six aces and did not face a break point all afternoon while breaking his rival twice.