He clocked 1:20.21s in a field of 56 walkers, bettering the old national record of 1:20.35s, which stood in the name of Gurmeet Singh.
Gurmeet finished 33rd with a timing of 1:23.34s while the third Indian in the fray, Baljinder Singh, was 43rd in 1:25.39s.
Irfan was placed 27th after the six-km mark but went ahead to fifth after eight kms. He could not maintain his place after that though he hung on to the leading pack for a while.
His performance was in improvement on his earlier personal best of 1:22.09s, which he recorded in the IAAF World Race Walking Cup in Russia [ Images ], in May.
All the three Indians had qualified for the Olympics after achieving the 'A' qualification standard.
Ding Chen of China won the gold in an Olympic record timing of 1:18:46s while the silver and bronze went to Erick Barrondo (1:18.57) of Guatemala and Zhen Wang (1:19.25) of China.