Luangnam ousted second-seeded Greta Arn 6-4, 3-6, 6-3 in a match that took 2 1/2 hours. Luangnam had five breaks, with three in the first set and two in the third.
Hampton was a 7-5, 6-1 winner over fourth-seeded and defending champion Zheng Jie by cashing in seven of her eight break-point chances. Hampton ended up winning 60 percent of the points off Zheng's serve.
Pauline Parmentier also came away with a win over a seeded player, stopping No. 7 Christina McHale 6-4, 6-1. She won 71 percent of the points on serve, losing just three points serving in the second set.
Other first-round results had Simona Halep defeating Arantxa Rus, 4-6, 6-3, 6-1; Johanna Larsson coming from behind for a 4-6, 6-3, 6-2 decision over Misaki Doi; Anastasija Sevastova claiming a 6-4, 6-7 (5-7), 6-4 win over Luksika Kumkhum; and Grace Min beating Maryna Zanevska 2-6, 6-4,6-3.
Also, Eleni Daniilidou defeated Coco Vandeweghe 1-6, 7-6 (7-5), 6-4 in a battle of wild-card entrants; Kirsten Flipkens topped Galina Voskoboeva 6-1, 6-7 (2-7), 7-5; Kiki Bertens took out Svetlana Kuznetsova 6-7 (5-7), 6-2, 7-5); and Elena Vesnina eliminated Eugenie Bouchard 7-5, 6-3.
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