SANDWICH (AFP) - Northern Ireland's Darren Clarke and American Lucas Glover took the clubhouse lead at the British Open on Friday as overnight front-runners Tom Lewis and Thomas Bjorn dropped off the pace. Clarke carded a two-under-par 68 for the second day running to move to four under at the halfway stage, while 2009 US Open champion Glover shot a solid level par 70 for a 36-hole total of 136. Bright sunshine and the gentlest of breezes made the demanding Royal St George's links layout a far more attractive proposition on Friday, a day after powerful off-shore gusts had buffeted the course. Clarke's round was a roller-coaster with an eagle and five birdies offset by a double-bogey and three bogeys but the 42-year-old Ulsterman was bullish about his prospects heading into the weekend. "It would mean an awful lot, but obviously this is only after two rounds," he replied when asked what a win in his 20th Open would mean to him. "There's an awful long way to go yet, and I believe the forecast for the weekend is very, very poor, which I quite look forward to. 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, and will be." Cigar-chomping Miguel Angel Jimenez was on course to join Glover and Clarke at the top of the leaderboard, with the Spaniard four under through 15 holes. Overnight leader Bjorn meanwhile followed up his first round 65 with a two-over-par 72 which left him one off the lead at three under. Two other players, US PGA champion Martin Kaymer and American Chad Campbell were tied with Bjorn for fourth after carding 69 and 68 respectively, just ahead of five players grouped together on seven under. Tournament favourite Rory McIlroy meanwhile was frustrated in his efforts to mount a sustained second day charge. The 22-year-old US Open champion, who had started the day one over, looked to be getting into an ominous groove after back-to-back birdies on the sixth and seventh took him to one under. But bogeys on the eighth and 10th checked his advance and the Northern Irishman remained one over after 12 holes, five adrift of the leaders. English amateur Lewis meanwhile slipped down the pecking order after a four-over-par 74 which left him at one under along with four other players. Yet with the cut projected to come at three-over, Lewis, 20, has done enough to ensure his involvement over the weekend, which is more than can be said for some illustrious names facing elimination. Among those who face being cut are English world No.2 Lee Westwood, who never got going on his way to a three-over-par 73 which left him four over. Westwood's hopes of winning a first Major were effectively torpedoed on the front nine, where he racked up a double-bogey and three bogeys. Last year's US Open champion Graeme McDowell is also heading for the exit after a shocking seven-over-par 77 that featured a double-bogey and five bogeys. "I just can't string four rounds together at the minute, and this week I couldn't even string two together," a dejected McDowell said. World number one Luke Donald meanwhile was flirting dangerously close to the cutline at two over par through 10, three over for the tournament. The biggest cheer of the morning went to 61-year-old American legend Tom Watson who scored a hole-in-one at the par-three sixth hole with a four iron. Watson eventually shot a level par 70 to finish at two over after 36 holes.