On a sun-drenched, windswept afternoon in mid-December, as temperatures hovered well below zero, two men crossed the finish line of the 18th annual Antarctic Ice Marathon hand-in-hand, taking seventh place in the 26.2-mile run, the world’s southernmost race.

One was Simon Messner, the 33-year-old son of Reinhold Messner, the legendary Italian mountaineer who was the first person to reach the summit of all 14 of the world’s 8,000-meter (26,250-foot) peaks. The other was Laurent Lecamp, 46, managing director of the watch division at Montblanc, the German luxury pen and watchmaker named for the highest point in Western Europe.

Dressed identically, including black stocking caps and blue parkas, both men also wore the Montblanc 1858 Geosphere 0 Oxygen South Pole Exploration, a wristwatch whose icy blue dial matched the colors of the surrounding glaciers.

“We managed in four hours, 29 minutes, 22 seconds,” Mr. Lecamp said by video call from his home in Geneva, one week after the race. “And we did it together with the Montblanc South Pole on the wrist.”

Over the past century, wristwatches have accompanied explorers to the ends of the earth and beyond, from the Rolex that Edmund Hillary and Tenzing Norgay carried on their 1953 ascent of Mount Everest to the Omega Speedmaster that Buzz Aldrin was wearing in 1969 when he became the second man to walk on the moon. And among some hard-core athletes and explorers, mechanical timepieces still are considered essential tools.

Mr. Lecamp said that became clear to him at Union Glacier Camp, their accommodations in Antarctica, where his wristwatch was an object of curiosity among his fellow marathoners.

“All the runners, they observed us like extraterrestrials,” Mr. Lecamp said. “They all had connected watches.

“But there was a big issue with the connected watches: The battery cannot last very long when it’s cold. All of them went to a specific place for charging. And the only people with no need to charge their watch were Simon and me.”

On a follow-up call in late December from his farm in the Dolomites, Mr. Messner, a Montblanc ambassador since 2022, said the watch, a limited edition of 1,990 pieces, was meaningful to him for a couple of reasons. Not only was it inspired by his father’s historic 1,740-mile, 96-day crossing of the Antarctic landmass in 1990, when the elder Mr. Messner and the German explorer Arved Fuchs became the first men to cross the continent by foot without animal or motorized support, it also kept him company on his own Antarctic journey.

“Running a marathon is very different from crossing a continent, but you feel it,” he said. “It was very emotional.”

The idea to run the marathon was Mr. Lecamp’s. An ultra-trail runner and veteran marathoner, the Swiss watch executive has participated twice in an ice marathon across Lake Baikal in Russia, in 2018 and 2019. (The first race, however, was cut short because conditions were deemed too dangerous.)

When he invited Mr. Messner to join him in Antarctica, Mr. Lecamp insisted that they run the entire course together. Mr. Messner, an accomplished alpinist who scaled Mont Blanc in 2022 wearing a previous version of the 1858 Geosphere watch, was game.

“I generally see life consisting of possibilities, and this was just another possibility to know my body a bit better,” Mr. Messner said. “It was different from mountaineering. Normally, when I climb, there are a lot of fears and they were totally missing.”

On the day of the race, he was focused on time. “I’m not always wearing a watch while mountaineering, but when running a marathon, it makes much more sense because time counts,” Mr. Messner said. “The great thing about the watch I wore in Antarctica was the lightness. I don’t know of another automatic watch that’s this light.”

Introduced in November, the $7,800 timepiece has a 42-millimeter titanium case and weighs 126 grams (4.4 ounces). It contains no oxygen, so it will not fog up during drastic temperature changes, and its components will last longer and provide greater precision over time.

Mr. Lecamp said he appreciated having the zero-oxygen watch at the camp, when he noticed that the dial of another runner’s mechanical timepiece became misty when he came out of his tent.

“His watch had humidity appearing due to the oxygen that was inside,” Mr. Lecamp said. “He couldn’t even read the famous name on his wrist.”