Padraig Harrington and Swede Daniel Chopra found former Open champion Ben Curtis a tough man to catch in the third round of the US Tour's Booz Allen Classic today.

Curtis, who went into a slump following his shock victory at Sandwich in 2003, resumed one ahead of Argentina's Jose Coceres.

But while Coceres fell away to a nightmare six over par for the first 11 holes, Curtis played them in three under and on 18 under led fellow American Brett Quigley by four.

Chopra, seeking his first victory in the circuit, was four under for the day, with six remaining, and had climbed into joint third spot, but was still six adrift.

Harrington, joint ninth overnight, improved from seven under to 10 under with five left and had only one bogey in 32 holes, but had slipped to joint 10th.

The round had been brought forward because of the threat of bad weather, the leaders teeing off at 9am local time in Potomac.