Competing in just the third 50km race of his career and the first one in two years, Palma was inspired to compete in his native state of Michoacán in a race that was also part of the International Association of Athletics Federations (IAAF) Race Walking Challenge

The 28-year-old set the leading pace from the beginning and reached the first 10km in 45min 55sec, 25 seconds ahead of his compatriot Horacio Nava and 2017 Pan American Cup champion Claudio Villanueva of Ecuador.

His lead increased to a minute-and-a-half as he hit the 20km mark in 1 hour 31min 24sec and, despite slowing down by almost a minute between 42km and 48km, he regained a more consistent pace to win in 3:49:39 - almost eight minutes faster than his personal best.

Colombia's Jorge Armando Ruiz came from behind and overtook Nava in the last lap to secure the silver medal in 3:56:07.

Nava, a three-time Olympian at the distance, finished third in 3:56:39. 

"It is a great day today, to win at home in front of such a great crowd," Palma said.

"That’s the result I expected. 

"I trained at high altitude in Mexico City and all my sacrifice paid off."

It was Palma's second IAAF Race Walking Challenge win after dominating the 20km in Chihuahua in 2013, also on home soil.

In the women’s field, Brazil’s Viviane Santana set the early pace, but eventual winner Inga bided her time. 

The 21-year-old moved to the front at 20km, covered in 1:42:52, and never looked back to achieve a breakthrough performance on her debut at the distance.

Inga, the 2017 Pan American under-20 bronze medallist, crossed the finish line in 4:22:57 and improved the national record by almost 20 minutes. 

She became the second Peruvian to take an IAAF Race Walking Challenge victory, two years after Kimberly García won in Rio Maior in Portugal.

Inga also joined García as the only two Peruvians to take the Pan American Cup, six years after her fellow countrywoman's victory in Guatemala.

Ecuadorians Johanna Ordoñez and Magaly Bonilla, sixth and 11th respectively at the 2018 IAAF World Race Walking Team Championships, followed home to complete a South American medal sweep with times of 4:24:49 and 4:33:52. 

Defending champion Nair da Rosa of Brazil finished eighth. 

In two years, the number of female competitors at 50km has risen from three to 16.

The Pan American Cup drew 170 athletes from 22 countries in its return to Mexico for both distances after 29 years.

It was the fifth leg of the 11-race IAAF Race Walking Challenge series, which is due to resume in Chinese city Taicang on May 11 and 12 and conclude in October with the Around Taihu International Race Walking in Suzhou, also in China.