LISBON, October 12, 2013 (AFP) - The 29-year-old Scottish player hit 11 birdies in the first 17 holes and needed another on the last to break 60 but a chip from 15 feet grazed the edge of the hole before he had to putt for a par.
Jamieson had shot a round of 57 before winning his first title at the Nelson Mandela Championship in South Africa last December, but that was in a tournament cut to 36 holes on a course reduced to a par 65 because of wet fairways.
"I said to Richard (his caddie) playing 17 I really want to make a birdie here so we have a chance of it going down the last and I could not have asked to hit a better shot in," he said.
"It pitched just short of the hole."
It was the 18th round of 60 in European Tour history and the second this season after Peter Uihlein's 12 under round during the Alfred Dunhill Links Championship.
England's Paul Waring, seeking his first title, leads in Portugal by two shots after carding a 67 for a 16 under par total.
Jamieson, on 14 under, shares second place with Hennie Otto, Simon Thornton and Jamie Donaldson.
Leading third round scores in the Portugal Masters at the Oceanico Victoria Golf Course, Algarve, Portugal, on Saturday (GBR/IRL unless stated, par 71):
197 - Paul Waring 67 63 67
199 - Hennie Otto (RSA) 66 64 69, Jamie Donaldson 65 68 66, Simon Thornton 65 69 65, Scott Jamieson 66 73 60
200 - Christopher Doak 67 64 69, Alvaro Quiros (ESP) 65 67 68, Pablo Larrazabal (ESP) 69 67 64
201 - Justin Walters (RSA) 69 63 69, Bernd Wiesberger (Aut) 66 65 70
202 - Robert Coles 67 71 64, Stephen Gallacher 70 67 65, Nicolas Colsaerts (BEL) 68 67 67, Matthew Baldwin 67 66 69, Jose Manuel Lara (ESP) 67 69 66
203 - Francesco Molinari (ITA) 68 72 63, David Lynn 65 65 73
204 - Robert Jan Derksen (NED) 69 68 67, Chris Wood 66 71 67, Ross Fisher 67 66 71, Martin Kaymer (GER) 68 68 68, Raphael Jacquelin (FRA) 71 66 67
205 - Soren Kjeldsen (DEN) 69 65 71, Danny Willett 69 67 69, Tom Lewis 70 67 68, Ricardo Gonzalez (ARG) 72 68 65, Anthony Wall 68 68 69, Felipe Aguilar (CHI) 65 70 70, Romain Wattel (FRA) 71 67 67, Alexandre Kaleka (FRA) 72 65 68
Selected:
207 - Garth Mulroy (RSA) 70 69 68, Andrew Dodt (AUS) 72 66 69
208 - Richard Green (AUS) 71 69 68, Paul McGinley 71 66 71
209 - Thomas Bjorn (DEN) 74 63 72, Miguel Angel Jimenez (ESP) 71 69 69
210 - Thomas Aiken (RSA) 71 69 70, Jaco Van Zyl (RSA) 69 67 74