While the Scot set off with back-to-back bogeys, England's Foster birdied both holes from 12 and 40 feet and at 13 under par led by two from compatriot Kenneth Ferrie, Saturday's 60-shooter.
The gap then became three when Ferrie bogeyed the 305 yard third to slip alongside Lawrie on ten under.
Foster threw the event wide open again with three successive bogeys from the fifth. He drove against a tree at the first of them, three-putted the next and then came up short of the green on the seventh.
At ten under he was in a tie with Chilean Felipe Aguilar, who covered the first nine in a two under 32, and one in front of not only Lawrie, who had his third bogey at the fifth, but also last week's winner Raphaël Jacquelin, England's European Tour rookie Matthew Nixon and Swede Johan Edfors.
Foster and Aguilar found themselves part of a four-way tie when Edfors and then Lawrie birdied the 398 yard 10th, Foster missing from inside four feet there.
Jacquelin had missed from even closer at the short ninth, but chipped in two holes later to be only one behind again again with Nixon and Dane Jeppe Huldahl.
Lawrie turned his day around by making it three birdies in a row and with six to play was one in front of Edfors and two ahead of Foster and Aguilar.