American teenager Learner Tien beats Alexander Zverev, advances to the Acapulco quarterfinals

ACAPULCO, Mexico (AP) — American teenager Learner Tien beat top-seeded Alexander Zverev 6-3, 6-4 on Wednesday to move into the quarterfinals of the Mexican Open in Acapulco

It was his second career win over a top-five player. The 19-year-old from California defeated Daniil Medvedev (5) in the second round of the Australian Open in January when he reached the fourth round.

The left-handed Tien is the youngest player to win his first two matches against top-five opponents.

"I just went out there and tried to control my side of the court," Tien said in comments on the ATP website. "Obviously I knew it was going to be a tough match. To come through feels great... I think just focussing on what I can control and keeping my cool as best as I can has really taken me a long way."

Tien is next playing eighth-seeded Tomas Machac, who advanced after beating Daniel Altmaier 7-6 (3), 6-1.

In his South American matches recently, Zverev lost in the first round in Argentina and in the quarterfinals in Brazil.

The third day of play in Acapulco saw three seeded players quit with an illness. One of them was Holder Rune (4), who left his match against Brandon Nakashima down 3-0 in the first set.

Nakashima will play against David Goffin, who defeated American Ben Shelton 7-6 (3), 6-3.

"Furious and so sad at the same time. Had a food poisoning and was unable to play today," said Rune on X. "One of my favorite places is Mexico and I love this tournament. Absolutely not the way I wanted it to end."

Tournament organizers have not said if the other players who retired suffered from the same ailment as Rune. Second-seeded Casper Ruud also could not play against Mexican Rodrigo Pacheco.

The other player who got sick in Acapulco was third-seeded Tommy Paul, who pulled out before his match against Marcos Giron to give his countryman a walkover.

Giron will next play Denis Shapovalov, who had a 6-4, 6-3 win over Alex Michelsen.