Robertson fired a 2-under-par 70 to move to 12-under-par on a day when players blazed around the course.
The leaderboard resembled gridlock on the New Jersey turnpike, with 11 players within three strokes of the lead. Robertson's nearest challengers were a group of six players at 11-under-par, including six-time major winner Nick Faldo and fellow Englishman and defending Dunhill champion Anthony Wall.
Former amateur prodigy Justin Rose also moved to 11-under with a 5-under-par 67, while the unsung pair of Argentine Ricardo Gonzalez and South African Des Terblanche also moved to 11-under after rounds of 64 and 65, respectively.
Young Australian Adam Scott posted a round of 6-under 66 to become the sixth player to move to 11-under through 36 holes.
'It was always going to be more difficult today. I told myself that all I needed to do was start well - I failed miserably in achieving that goal,' Robertson said after bogeys at the second and third.
'I'm still battling with the long game but I managed to turn at level par and I'm happy with the score I posted because I suddenly had the pressure of the tournament on me.'
Faldo was thrilled with his round after enduring the leanest spell of his professional career. He has not won a tournament for four years - the Nissan Open in early 1997 - and his last victory on the European Tour was in 1994.
'It was a great day. I don't think I've been six-under after 12 holes for a long time,' an elated Faldo said. 'I've got to take a full run at it on the weekend and try and keep it nice and simple and keep the putter hot.'
Wall was equally pleased with his joint low round of the day of 64, which was also his lowest round as a professional golfer.
'I've always loved Houghton and this tournament,' Wall said. 'It reminds me of home and the conditions are so good that you can't wait to get out there.
'This is a course where you have to think your way around and shape your shots. There are a few old trees that hang over greens and it is not all about power.'
Wall said that part of his improved game was the fact that he has been working with a nutritionist in England and started to relax more when traveling.
'I get quite uptight waiting at airports and queues and with the improved diet and exercises I've been doing it has helped,' Wall said.
'After winning here last year I feel that I belong on tour, because you always feel as if you've got to impress people and winning changed that.'
Terblanche described his game as well rounded after his recent good showings on the Sunshine Tour. 'I think a little bit of everything is working for me at the moment,' he said.
'I'm staying out of trouble with the long shots and I seem to have found the pace of the greens, which helps because you don't have too many of those awkward four and five-footers for par.'
Rose, who has struggled as a professional, felt that the pieces have started to come together after putting in long hours on the practice range. His halfway total of 11-under-par is the lowest he has been midway through a tournament.
South African David Frost was penalized two-strokes for being late for his tee time, which dropped him from 3-under to 1-under and in the process led to him missing the cut, which was made at 141, 3-under-par.
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