LISBON, October 10, 2013 (AFP) - The Spaniard, who was the champion on the Algarve in 2008 but whose career was interrupted by wrist surgery last year, suffered two bogeys early in his round.
But he stormed back with an impressive run on the home stretch to card a six-under 65.
He shares the lead with Felipe Aguilar, Jamie Donaldson, David Lynn, Max Kieffer, Graeme Storm and Simon Thornton.
"It was a good fight after being two over after five holes," said the 30-year-old Quiros, who now lives in Portugal.
"I was putting beautifully and that was the key.
"This is my second home tournament and now that I'm living here I have to consider Portugal home. It's always good, this event has been special since I've been coming here."
Donaldson, who played in the Seve Trophy last week, was seven under before three-putting the eighth, for his only bogey.
Lynn picked up three shots in his last five holes.
"It was good playing under tough competitive conditions so it's nice to play well and just bring it on to this week," said Donaldson.
Lynn, who also featured in the Seve Trophy last, has been suffering with flu.
"I keep taking medication but a 65 cures any ailments," he said.
Leading first round scores in the Portugal Masters at the Oceanico Victoria Golf Course, Algarve, Portugal, on Thursday (GBR/IRL unless stated, par 71):
65 - Felipe Aguilar (CHI), Maximilian Kieffer (GER), Jamie Donaldson, David Lynn, Simon Thornton, Graeme Storm, Alvaro Quiros (ESP)
66 - Hennie Otto (RSA), Chris Wood, Mark Tullo (CHI), Soren Hansen (DEN), Marcel Siem (GER), Scott Jamieson, Andy Sullivan, Bernd Wiesberger (AUT), Julien Quesne (FRA)
67 - Ross Fisher, Paul Waring, David Horsey, Matthew Baldwin, Victor Dubuisson (FRA), Jose Manuel Lara (ESP), Seve Benson, Robert Coles, Tommy Fleetwood, Alejandro Canizares (ESP), Eddie Pepperell, Fredrik Andersson Hed (SWE), Christopher Doak
68 - Anthony Wall, Francesco Molinari (ITA), Joost Luiten (NED), Matteo Manassero (ITA), Nicolas Colsaerts (BEL), Martin Kaymer (GER), Michael Hoey
69 - Soren Kjeldsen (DEN), Richard Bland, Robert Jan Derksen (NED), Jean-Baptiste Gonnet (FRA), Anders Hansen (DEN), David Howell, Jorge Campillo (ESP), Jaco Van Zyl (RSA), Danny Willett, Pablo Larrazabal (ESP), Paul Lawrie, Eduardo De La Riva (ESP), Justin Walters (RSA), Andreas Harto (DEN), Gonzalo Fdez-Castano (ESP)
Selected:
70 - Garth Mulroy (RSA), Keith Horne (RSA), Park Jun-sub (KOR)
71 - Thomas Aiken (RSA), Brandon Stone (RSA), Miguel Angel Jimenez (ESP), Richard Green (AUS), Paul McGinley, Andrew Dodt (AUS)
73 - Shiv Shankar Prasad Chowrasia (IND), Thongchai Jaidee (THA)
79 - Dawie Van Der Walt (RSAa)