The Open 2011: Darren Clarke & Lucas Glover share halfway lead

Northern Ireland's Darren Clarke and American Lucas Glover head into the weekend with a one-shot lead at the 140th Open Championship.

Clarke shot a two-under 68 and 2009 US Open champion Glover carded 70 to set the pace at four under on a glorious summer's day at Royal St George's.

They head joint overnight leader Thomas Bjorn (72), Chad Campbell, Martin Kaymer and Miguel Angel Jimenez.

Luke Donald and Lee Westwood, the world number one and two, missed the cut.

Former major champions Padraig Harrington, Graeme McDowell, Ernie Els and Angel Cabrera were other big names to make an early exit.

Ian Poulter (+7), Ernie Els (+8), world number eight Matt Kuchar and 2003 winner Ben Curtis (both +11) were also eliminated.

Masters champion Charl Schwartzel, 1996 Open winner Tom Lehman, US Ryder Cup captain Davis Love, American Dustin Johnson, Spain's Pablo Larrazabal, Dane Anders Hansen and South African George Coetzee all ended two under.

US Open champion Rory McIlroy had four birdies and three bogeys in a 69 to finish level par.

Clarke was one of the early starters on day two and admitted the weather conditions helped his cause as an eagle, five birdies, three bogeys and a double bogey left him at four-under-par.

"It had a bit of everything. Good shots, good putts, poor shots and poor decisions," Clarke told BBC Sport. "Overall I am very pleased with a 68.

"We had the good side of the draw, there was no breeze this morning.

"To have all the support is great. It is nice to play well again and hopefully contend over the weekend at the biggest tournament in the world."

Having finished second in 1997 and third four years later, Clarke would love to become the third major champion from Northern Ireland, following on from the success of McDowell and Rory McIlroy at the last two US Opens.

"To have back-to-back US Open champions from a little country like Northern Ireland, that's a massive achievement," he said.

"It hasn't really affected me apart from being proud that I'm from the same place as they are and I may have given them a little bit of a helping hand here and there on the way up."

He added: "I believe the forecast for the weekend is very, very poor. I quite look forward to that, but the course is going to play very, very tough.

"If that's the case, then the tournament is still wide open for an awful lot of players."

Amateur Tom Lewis, the joint first-round leader, is still the leading Englishman but he endured a tougher time as he added a 74 to his opening 65 for a halfway total of one under. The 20-year-old still has a fight on his hands with American Peter Uihlien - two over after a pair of 71s - for the leading amateur's Silver Medal.

Lewis was playing with five-time champion Tom Watson, 61, who fired a hole-in-one with a four iron on the short sixth en route to a round of 70 for two over.

American Phil Mickelson, the former world number two, kept himself in the hunt for a first Open title with a 69 to end one under. His young countryman Rickie Fowler, playing with McIlroy, added a second 70 for level par alongside Spain's Sergio Garcia (70).