Jose Manuel Lara posted a 7-under 65 during round two to move into a tie for second with Nicolas Colsaerts (70), Philip Golding (70), Anders Hansen (66) and David Howell (65) at 8-under-par 136.
Bjorn started quickly with back-to-back birdies from the 10th on the Albatross Course at Le Golf National. He picked up his third birdie at the par-4 13th and moved to minus-6 with a birdie at the 15th.
The Dane birdied the 18th for the second straight round to make the turn at 7-under. He continued his move up the leaderboard with birdies at No. 3 and 5.
However, Bjorn stumbled to his lone bogey of the day at the par-4 seventh, his second on that hole during this tournament. He came back in fine fashion as he capped his round with back-to-back birdies from the par-3 eighth to move to the top of the leaderboard.
'I know I have the golf game and think my best game is among the best in the world but I don't perform my best all the time,' said Bjorn. 'I don't know why. I seem to play my best when I get into a routine of playing a lot of tournaments and playing courses I enjoy. I am going into that now, playing nine out of ten weeks and I am looking forward to it.'
Bjorn is hoping to continue the trend of excellent of play by Danish golfers.
'We have a generation of Danish players that are very good,' said Bjorn. 'We are very fortunate to have not one or two players but four players around the same age as well as Steen Tinning who has won a couple of times. But we have four players who work very hard. That's the way we used to look at the Swedes.'
Soren Kjeldsen, a fellow Dane, won the Diageo Championship last week. Hansen, another Dane, shares second behind Bjorn.
'Soren's win last week was a wake up call for all of us,' Bjorn said. 'I think both Soren and Anders Hansen got here very determined. There is a different look in their eyes. Kjeldsen got left out last year not winning and he went out this year determined, working harder than probably anyone on this tour and got what he deserved.'
Anders Hansen posted six birdies and a bogey to move to 8-under.
'I worked really hard for two weeks so it is not just because Soren has won,' said Hansen. 'Obviously him winning gives us a boost and maybe we should start playing well. I have struggled with my putting but found something over the last couple of weeks and it makes a change to hole some.'
Stephen Gallacher and Justin Rose share seventh place at 7-under-par 137. Barry Lane and Pierre Fulke are among eight players tie at minus-6.
The cut line fell at 1-under-par 143 with 78 players moving on to the weekend. Malcolm MacKenzie, the defending champion, missed the cut after rounds of 76-77 to come in at 9-over-par 153. Eric Chaudouet, an amateur who shared the first-round lead, struggled to a 5-over 77 Friday but survived right on the cut line of minus-1.