Lahiri was two shots better than John Senden and three better than Reteif Goosen, among those who had finished the first round. Tim Wilkinson was at four-under with two holes to go.
Lahiri had three birdies on either side and he birdied three of the four par-fives.
If Lahiri keeps the lead at the end of the round, it will only be the second time he will hold sole or shared lead after 18 holes.
Lahiri's longest putt was the 17-foot birdie on the 15th and his other birdies were all inside 10 feet, indicating how good his hitting was today.
Lahiri's hitting and putting were quite easily the highlight for him and sets him for a good week.
Rory McIlroy, Patrick Reed and Jim Furyk were among those who shot 73 each.
McIlroy struggled at four-over through 13 holes, before fighting back to 73.
