Scotland's Liam Johnston revealed he was blissfully unaware of his opportunity to card only the second 59 in European Tour history after setting a blistering pace at the Portugal Masters.
At the same venue where Oliver Fisher made history in 2018, Johnston went to the turn in 31 before firing five birdies in his next seven holes to leave him needing an eagle-birdie finish to break the magical 60 barrier.
The 27-year-old from Dumfries found the green in two on the par-five 17th, but left his eagle attempt short of the hole and was unable to find an unlikely two on the difficult par-four 18th.
A 10-under-par 61 beat his previous lowest score on the European Tour by six shots and gave Johnston a one-shot lead over France's Julien Guerrier on a day of typically low scoring at Dom Pedro Victoria Golf Course in Vilamoura.
“I had no idea,” Johnston said when asked if a 59 had been in his sights. “I thought it was a par 72, but I was obviously trying to hole the putt on 17 for eagle but left it a little bit short before making a nice par on the last.”
“I told my coach that I was swinging it as good as I have. My game feels as it is really trending in the right direction and, more importantly, I have really improved mentally. I wouldn’t say I felt a round like this has been coming, but I have been playing well.
“With the rough out there it was nice to keep the bogeys off the card. I saved well when I needed to, holing a lot of good putts out there, and I am delighted with the 10 birdies.”
Guerrier carded nine birdies in his bogey-free 62, with England's Laurie Canter two shots further back following a 64.
Northern Ireland's Jonathan Caldwell made five birdies in his final seven holes to sit fourth overall after he signed for a six-under 65.
Cormac Sharvin included an eagle at the par-five fifth in his opening round of one-under 70, while Gavin Moynihan opened with a level-par 71.
Pre-tournament favourite Tommy Fleetwood carded a three-under-par 68 containing five birdies and two bogeys, the last of which came following an uncharacteristic hooked drive into the water on the 18th.
“The back nine was probably the best I’ve hit my irons for a long time,” Fleetwood said.
“I practised putting late last night and the green was burnt to a crisp and I think that put me off a little bit. I thought they were going to be rapid and at times I was a little bit weak with my pace.
“Overall I was happy. I had a dodgy spell and then started hitting it well and had chances. The course is a different test to what it’s always been. I drove it great, ignoring the one on the last, and gave myself a lot of chances.”
Defending champion Steven Brown matched Fleetwood's 68.
British and Irish unless stated, par 7):
61 Liam Johnston
62 Julien Guerrier (Fra)
64 Laurie Canter
65 Jonathan Caldwell
66 Sebastian Soderberg (Swe), Matthew Jordan, Thorbjorn Olesen (Den), George Coetzee (Rsa)
67 Richard Bland, Lucas Bjerregaard (Den), Sihwan Kim (Kor), Paul Waring, Ryan Fox (Nzl), Brandon Stone (Rsa), Guido Migliozzi (Ita), Francesco Laporta (Ita), Adrien Saddier (Fra), Dale Whitnell, Masahiro Kawamura (Jpn), Nino Bertasio (Ita)
68 Marcus Armitage, Steven Brown, Tomas Guimaraes Bessa (Por), Jorge Campillo (Esp), Martin Simonsen (Den), Tommy Fleetwood, Bryce Easton (Rsa), Antoine Rozner (Fra)
69 Ben Evans, David Law, Ricardo Gouveia (Por), Adrian Meronk (Pol), Joakim Lagergren (Swe), Rhys Enoch, Ashun Wu (Chn), Tom Gandy (IOM), Pablo Larrazabal (Esp), Jason Scrivener (Aus), Jose-Filipe Lima (Por), Julian Suri (USA), Jack Senior, Johannes Veerman (USA), Matthieu Pavon (Fra), Matthew Southgate, Jamie Donaldson, Ricardo Santos (Por), Marcel Schneider (Ger)
70 Sebastian Garcia Rodriguez (Esp), Alexander Bjork (Swe), Garrick Porteous, Emilio Cuartero Blanco (Esp), Tomas Santos Silva (Por), Robin Roussel (Fra), Wil Besseling (Ned), Max Schmitt (Ger), Robert Rock, Tapio Pulkkanen (Fin), Alejandro Canizares (Esp), Cormac Sharvin, Kristoffer Broberg (Swe), Niklas Lemke (Swe), Raphael Jacquelin (Fra), David Drysdale, Wilco Nienaber (Rsa), Scott Vincent (Zim)
71 Jens Fahrbring (Swe), David Howell, Joost Luiten (Ned), Gonzalo Fernandez-Castano (Esp), Vitor Lopes (a) (Por), Lars Van Meijel (Ned), Oliver Fisher, Gavin Moynihan, Andres Romero (Arg), Thomas Bjorn (Den), Nacho Elvira (Esp), Gregory Havret (Fra)
72 Zach Murray (Aus), Marcus Kinhult (Swe), Anton Karlsson (Swe), Maximilian Kieffer (Ger), Haydn Porteous (Rsa), Richard McEvoy, Grant Forrest, Rikard Karlberg (Swe), Carlos Pigem (Esp), Ben Stow, Jake McLeod (Aus), Pedro Figueiredo (Por), Dave Coupland, Pedro Lencart Silva (Por), John Catlin (USA)
73 Nicolai Von Dellingshausen (Ger), Kalle Samooja (Fin), Sebastian Heisele (Ger), Toby Tree, Daan Huizing (Ned), Alvaro Quiros (Esp), Robin Sciot-Siegrist (Fra), Shubhankar Sharma (Ind), Jose-Maria Olazabal (Esp), Joel Sjoholm (Swe), Calum Hill, Justin Walters (Rsa), Jordan Smith, Ewan Ferguson
74 Jean-Baptiste Gonnet (Fra), Joel Stalter (Fra), Will Enefer, Benjamin Poke (Den), Jonathan Thomson, Matthew Baldwin, Haotong Li (Chn), Peter Hanson (Swe), Maverick Antcliff (Aus), Andrea Pavan (Ita), Jbe Kruger (Rsa), Eduardo De La Riva (Esp), Benjamin Hebert (Fra), Lorenzo Gagli (Ita)
75 Wade Ormsby (Aus), Chris Paisley
76 Stephen Gallacher, Oliver Wilson
77 Ross Fisher, Darius Van Driel (Ned), Damien Perrier (Fra), Mathieu Fenasse (Fra), Jacques Kruyswijk (Rsa)
78 Steve Webster, Alexander Levy (Fra)
82 Miguel Gaspar (Por)