Ben Curtis carded a six-under-par 65 to hold a one-shot lead over Jose Coceres at the halfway stage of the Booz Allen Classic in Maryland.

After watching Coceres fire a second consecutive round of seven-under 64, Curtis followed up his opening 62 with a 65 to end the day on 15 under at 127.

Defending champion Sergio Garcia withdrew on Monday due to a back injury, leaving Ireland's Padraig Harrington - 23rd in the world - as the highest ranked player in the field.

Harrington carded a one-under 70 in the opening round but hit top form with a 65 to end the day on seven-under and tied for ninth.

"Obviously when he gets a 14-under after two days, you know that he's going to play well on the weekend," Curtis said after his round. "So you obviously want to try to stay as close as you can.

"Obviously I would have taken anything pretty much under par today after yesterday's round. But after the shaky round I got calmed down a bit, got the putter going, and that's the reason why I'm sitting here."

Curtis, the 2003 Open champion, began the day with a one-shot lead over Jeff Gove and added four birdies on his final nine to grab the lead from Coceres.

Coceres, playing without a PGA Tour card and in just his fourth event of the season, had an early tee time and fired eight birdies.

The Argentine had just one bogey at the TPC of Avenel to get to 14-under on 128 and take a three-shot lead at the time.

Coceres, a winner on both the PGA and European Tours in his career, finished out of the top 125 on the money list in three of the last four years.

And last season he missed the cut in 15 of 22 events and was a long way from the form he had in winning two Tour events in 2001.

Jeff Gove signed for a three-under 68 and is in third place at 11-under on 131, while John Huston (65) and Brett Quigley (63) are tied for fourth a further stroke back.