Tien defeated Zverev 6-3, 6-4 in an hour and 28 minutes en route to his second top-5 win of the season. Learnen outplayed the third-time Major finalist on serve and return. The young gun dropped serve once and stole 41% of the return points.

Zverev, the top seed at the Acapulco Open, went down 6-3 6-4 to the 19-year-old American on Wednesday. Tien, who claimed a big win over Daniil Medvedev en route to reaching the fourth round at the Australian Open in January, came from 1-4 down to win the second set – and the match – by reeling off five straight games.

Alexander's latest setback came against the 19-year-old Learnen Tien in the second round in Acapulco. A teenager ousted the Australian Open finalist 6-3, 6-4 in an hour and 28 minutes for his second top-5 victory of the season.

World number two Alexander Zverev suffers a shock early exit from the Mexican Open with a straight-set defeat against teenage qualifier Learner Tien.

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