Top seed Zverev crashes out of Mexico Open first round

Zverev, winner of the Acapulco tournament in 2021, was sent packing 6-3, 3-6, 6-3 in 2hr 28min by world number 57 Altmaier.

After sharing the first two sets, Altmaier took control of the third set with an early break to take a 2-0 lead before holding for 3-0.

Zverev missed opportunities to break back in the fifth and seventh games, unable to convert any of three break points and Altmaier served out to clinch victory and set up a second round meeting with Serbia's Miomir Kecmanovic.

In other games on Tuesday, Australia's Jordan Thompson was brought back down to earth after losing his first round match just two days after winning the first ATP title of his career.

Thompson, who went on a giant-killing run before defeating Casper Ruud to win the Los Cabos Open final on Sunday, was ousted in three sets by American qualifier Aleksandar Kovacevic, losing 6-3, 5-7, 6-4 in 2hr 42min.

Kovacevic will play Holger Rune in the second round after the Danish second seed cruised past Michael Mmoh 6-2, 6-3 earlier Tuesday.

Greece's Stefanos Tsitsipas, the fifth seed, eased past Russian Roman Safiullin 6-3, 6-4.

Tsitsipas will play Italian qualifier Flavio Cobolli in the second round.

"It's one of those first rounds that you get good opponents and a very good, strong start from the beginning of the tournament," Tsitsipas said in an on-court interview after his win.

"I knew that dealing with Roman, he's someone that can play good on these kinds of surfaces. He takes the ball early, pushes you back.

"That was the main thing I had to deal with today, which I did pretty well."

Meanwhile, Sunday's beaten Los Cabos finalist Ruud, the sixth seed in Acapulco, needed three sets to overpower Christopher Eubanks, eventually winning 6-4, 6-7 (5/7), 6-3.

American eighth seed Frances Tiafoe defeated Australia's Max Purcell 4-6, 6-3, 6-0, and now faces Germany's Dominik Koepfer, a 6-4, 4-6, 6-0 winner over France's Terence Atmane.