PGA Tour rookie Webb Simpson defied difficult conditions in the second round of The Barclays at Liberty National to take a two-shot lead at the halfway stage, hours after Pádraig Harrington undid all his good work from the first round by shooting a 75.

The 24-year-old American shot a three-under-par 68 to move to eight under, two clear of countrymen Steve Marino and Paul Goydos, who both settled for level par.

With Tropical Storm Danny affecting the east coast of the US, most players struggled, but for Simpson it was a welcome return to form after missing 10 of his last 19 cuts having begun his PGA Tour career with two top-10 finishes.

Fredrik Jacobson and Heath Slocum tied for fourth at four under while England's Ian Poulter led the clubhouse for much of the day on three under despite only managing a one-over-par 72.

That was the same mark as Steve Stricker and Richard S Johnson, with Ernie Els one further back after an impressive 68, the joint best round of the day with Simpson.

Sergio Garcia had a day to forget after his 65 in round one, the Spaniard dropping to a tie for 11th after a 76.

Three-time major winner Harrington also struggled, a 75 leaving him on level par heading into the weekend. "I am used to it (the rain) but it doesn't mean I like it," said the Irishman afterwards.

Englishman Luke Donald, whose 69 was one of only four under 70, and world number one Tiger Woods were alongside him on level par.

Justin Rose's 72 ensured he made the cut, which should be enough to earn him a spot at next week's Deutsche Bank Championship at TPC Boston.

"I was in a precarious situation this week," said the Englishman. "Miss the cut and I don't advance. Make the cut and I'm pretty much assured.

"It was brutally hard. I played out of my skin today... I played as good as I can for one over."

Defending champion Vijay Singh was an early casualty, though, the Fijian shooting a second successive 75 to miss the cut by three.

Singh is a four-time Barclays champion, with wins at Liberty National and Boston last year earning him the FedExCup title.

Meanwhile, because of the threat of heavy rain from the remnants of the tropical storm, the start of the third round has been delayed until 10.48am local time (1548 BST).