The 29-year-old holed a 40-foot eagle putt at the third on Saturday and added three birdies on his back nine, including at the final two holes, to overhaul Sweden's Joakim Lagergren (71) at the top.
For the third day in succession the weather forced long delays to the event, with the course waterlogged in places during the morning as the final few players wrapped up a second round delayed by high winds.
Syme navigated the conditions perfectly and admitted he was "buzzing" after his round.
"Obviously a bonus to finish with a couple (of birdies) towards the end but overall really, really pleased," he added.
Compatriot Richie Ramsay (71) finished the round in a share of third place with Portugal's Ricardo Gouveia (73) and Italian Francesco Laporta (69), six shots off the lead and four behind Lagergren.
"Obviously there's a bit of a gap at the moment for me and Joakim but with the weather tomorrow it can change so much, so quickly," Syme said.
"I would love to do it, hopefully I can play my game tomorrow and I can do it. I'll just try to play one shot at a time and get that mindset from the start, and what will be will be."
Australia's Jason Scrivener (69) is in a nine-way tie for 13th at one under after a steady round including just three birdies and one bogey.
With AAP.
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