British Cameron Norrie sent packaging by teenagers in an open opening opening.
British no. 2 lost 7-6 (7-5) 6-3 to 19 year old, which was ranked 83 in the world in the world, in an hour and 52 minutes in Acapulc.
Tien made a strong start, leading 4-1 in opening before Norrie recovered and served for a set at 5-4. However, Brit was broken, and Tien also won a pause for a tie before taking control of the second set.
Norrie received her only previous meeting against Tien in Hong Kong at the beginning of this year, beating him in real sets, 6-3 7-5.
Tien will face the match winner between Aleksandar Zverev and Matteo Arnaldi in the second round.
The second seed late Ruud has reserved its place in the next round with 6-4 6-4 victory over French Arthur Rintorknech.
The third seeds Tommy Paul was released by last Canadian Gabriel Dialloa 6-2 6-2, while American Ben Shelton, fifth tournament seeds, fought next to Cobolli 7-6 (7-4) 7-6 (7-4) 7-6 (7-4) 7-6 (7-4) 7-4. The second round.
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