Robert Heffernan pulled away in the last 10 kilometers to win the gold medal in the 50-kilometer walk on Wednesday, giving Ireland their first world championship title in 30 years.
Heffernan's gold came 30 years to the day after Eamonn Coughlan won the 5,000 meters in 1983.
The walk began shortly after an early-morning storm and finished in warm sunshine 3 hours, 37 minutes, 56 seconds later, the time it took Heffernan to cover the grueling distance. He was fourth at last year's Olympics.
Mikhail Ryzhov of Russia took the silver, 1:02 behind, and Jared Tallent of Australia, silver medalist at the past two Olympics, had to settle for bronze, 2:07 back. He also won the bronze at the worlds two years ago.
Olympic champion and 2009 world gold medalist Sergey Kirdyapkin pulled out shortly before the championships.
Ryzhov and Tallent were among the early leaders that also included Ivan Noskov of Russia, Yohann Diuniz of France and Grzegorz Sudol of Poland, with the lead switching hands.
Heffernan joined the group halfway into the race and by the 37th kilometer he and Ryzhov were slightly ahead.
At the 40th, Heffernan had a 12-second lead over Ryzhov. He increased that to 18 seconds with five kilometers left.
The Irishman kept building his lead and was smiling broadly as he entered the sparsely filled Luzhniki Stadium on his own.
After wrapping himself with an Irish flag, he embraced his wife Marian. Angel Garcia of Spain, the 1993 champion and the oldest competitor at the championships at 43, finished 12th.
In other morning events, Dwight Phillips of the United States stayed on course for a possible fifth world title by qualifying for the final of the long jump. Phillips jumped 7.95 meters, his personal best this season.
But Phillips will have to do a lot better than that to win gold.
Eusebio Caseres led all qualifiers with a leap of 8.25 meters. Luis Rivera of Mexico, who leads the season's world list with a jump of 8.46, qualified at 8.04.
But Olympic champion Greg Rutherford of Britain, recovering from a hamstring injury, failed to make the final with a best effort of 7.87.
The favourites advanced in the women's 5,000, led by Olympic champion Meseret Defar of Ethiopia, who topped all qualifiers in 15:22.94. Defar was the 2007 champion in the distance and also has a silver and a bronze in past championships.
Ethiopian teammate and world-record holder Tirunesh Dibaba, who won the 10,000 on Sunday, decided not to go for the double.
Margaret Wangari Muriuki of Kenya pulled up with a hamstring injury.
Asbel Kiprop of Kenya, the defending 1,500-meter champion and the 2008 Olympic gold medalist, led all qualifiers for Friday's semifinals in 3:38.15.
Kiprop has been dominant this season, three seconds faster than anyone else. Silas Kiplagat, who beat Kiprop at the Kenyan trials, topped his group, ahead of Olympic silver medalist Leo Manzano of the United States.
In the women's hammer throw, Anita Wlodarczyk of Poland led the qualifiers with a throw of 76.18 meters, while former world champion and Olympic bronze medalist Betty Heidler of Germany failed to advance to the final.
World and Olympic champion Tatyana Lysenko of Russia was safely through.
There is no evening session on Wednesday.