They stand at nine-under-par 135 with a one-shot lead after 36 holes at Whistling Straits. Overnight leader Darren Clarke shot a one-under 71 and is tied for third with Ernie Els (70) and Briny Baird (69)at eight-under-par 136.
Tiger Woods' PGA Tour record of 128 consecutive cuts made was in serious jeopardy until he birdied the 16th and 17th holes to shoot a 69 and make the cut by a shot at even-par 144, nine shots back.
Leonard, the 1997 British Open champ, began on the back nine Friday and wasted little time in getting into red figures. Four birdies got him a share of the lead.
Singh, the 1998 winner of the Wanamaker Trophy, bogeyed his first hole but righted himself with four front nine birdies and soon he also shared the lead.