Robert MacIntyre saw a commanding four-shot overnight European Open lead wiped out by Germany's Bernd Ritthammer on Saturday.
A seven-under 65 in the second round of the European Tour event had given MacIntyre a healthy advantage, but the Scot was less impressive as the weekend began.
The 23-year-old was playing alongside Ritthammer, the world number 924, and saw the German pile on the pressure despite a relatively modest round of 70.
MacIntyre went two over, with three bogeys, as he missed birdie chances at the seventh, eighth and ninth.
And Ritthammer, who like MacIntyre is without a European Tour title to his name, secured a share of the lead on nine under par.
Paul Casey shot a 69 to move one shot behind, with Pablo Larrazabal and Matthias Schwab a stroke further back at seven under.
Xander Schauffele fell completely out of contention with a four-over 76 to move to two over, a shot behind Patrick Reed, whose tough week improved only slightly with a 71.