Rob Heffernan finished ninth in the 20km walk as Ding Chen of China took the gold medal in a new Olympic record of 1:18.46.
Heffernan, whose preferred race is the 50km version, completed the race in a personal best time of 1:20.18.
The Cork athlete remained in contention until the closing stages and but dropped off the lead group as Guatemala's Erick Barrondo took silver and China’s Wang Zhen took bronze.
Chen, 19, led from the 14km stage and pulled away from the pack to finish the race well clear.
Russia's Valeriy Borchin, the defending champion, had moved up to second by the 16km stage but collapsed with the finish in sight.
Chen picked up the pace to pull clear of the field and began high-fiving the crowd as he approached The Mall.
A late burst took Barrondo well ahead in second, with Wang 39 seconds behind the winner.