Marc Warren edged his nose back in front early on day three of the Portugal Masters in glorious conditions at Victoria Clube de Golfe.
The forecast for overnight storms had led to a delayed two-tee start and preferred lies but conditions were perfect by the time play got under way at 1100 with more low scoring in prospect.
Scot Warren had held the first-round lead and looked like he would carry the solo advantage into day three until defending champion Andy Sullivan produced a brilliant 61 on Friday afternoon.
An early birdie on the second moved Warren to 15 under after three holes, however, a shot clear of Padraig Harrington and Jens Fahrbring - who needs to finish second or better this week to have a chance of keeping his card.
Sullivan was then at 13 under alongside Raphaël Jacquelin and Mikko Korhonen.
Harrington had spoken after round three of how he thought the pressure of being at the top may stop the leaders from going seriously low but he showed no sign of nerves with a 30-foot putt for a birdie on the first that got him into a share of the lead.
Sullivan hit a perfect tee-shot on the opening hole but when he put his second to the left of the green in just about the roughest stuff you will find around the course, a dropped shot followed.
A birdie for Warren on the second then moved him back to where he has been for much of the week - in the solo lead - but Fahrbring also made a gain to stay just one shot off the summit.
At 116th in the Race to Dubai, Korhonen needs a big week to keep his playing privileges and he made back-to-back birdies on the second and third to join Sullivan at 13 under.
Warren produced a snap hook off the third tee but did will to make his par while Jacquelin moved up the leaderboard with birdies on the second and third.
Anders Hansen, David Horsey, Joakim Lagergren and Callum Shinkwin were at 12 under, a shot clear of a large group including card-chasers Oliver Fisher, Trevor Fisher Jnr and Brett Rumford.
