Singh -- who has won more tournaments after turning 40 than any other player in history, but is winless this season -- finished 36 holes at the Firestone Country Club in 7-under 133.

Mickelson reached 134 by also firing a 66. Sean O'Hair, Peter Lonard, Lee Westwood and 2007 Masters champion Zach Johnson were all at 135.

With Tiger Woods out of action due to knee surgery, a renewal of the Singh-Mickelson rivalry could give golf a spark as the season winds down.

At the 2005 Masters, Singh asked a rules official to see if Mickelson's spikes were causing damage to the greens. Mickelson had a confrontation with Singh following that round.

Singh, who will be paired with Mickelson for Saturday's third round, said he thought that incident was behind them.

"It'll be nice," Singh said. "I think we'll have a good time."

First-round leader Retief Goosen shot a 71 to fall into a tie for 12th place.