Before the Welshman had teed off, the field closed in with England's Matthew Baldwin and Tommy Fleetwood and Donaldson's fellow Ryder Cup hopeful Stephen Gallacher all joining Frenchman Bourdy on eight under par.
The World Number 29 Donaldson responded in style, hitting a brilliant second shot to six feet at the par five opener and holing the eagle putt, before firing an iron to five feet at the fourth for another birdie.
At 12 under par he led by four from Dane Søren Kjeldsen, American David Lipsky and England's Garrick Porteous.
Lipsky was four under through 11, Kjeldsen holed a 15 footer at the third for consecutive gains, while former Amateur Champion Porteous converted a monster putt at the fifth.
Earlier Baldwin had made the greatest move – full of confidence having already registered four top-five finishes on this season's Race to Dubai, the 28 year old went to the turn in 32 and birdied three of the next four holes to be seven under for the day, only to then bogey the 14th and 16th.
Gallacher, who needs to garner as many Official World Golf Ranking points as possible to try and deny the likes of Graeme McDowell and Ian Poulter an automatic spot on Paul McGinley's side, birdied the long first but bogeyed the third and fourth to slip six shots off the pace.
The third player looking to make Europe's Team, Dutchman Joost Luiten, turned in 38 and in all likelihood was in need of a big performance at next week's Italian Open, the final event of the points race.
Donaldson dropped a shot at the fifth after three-putting, but got it back with a birdie at the short seventh.
However, things started to unravel at the eighth, where the two-time European Tour winner missed the green to the right, failed to get his first pitch to the green from some thick rough and left his next chip six feet short, missing the putt to run up a double bogey.
At ten under par his lead was down to one over Kjeldsen and Lipsky, who birdied the 14th and ninth simultaneously.