Opening day at Vilamoura belongs to Scotland's Warren

The 35-year-old began with six successive birdies at Victoria Clube de Golfe before adding a further three after blemishing his card slightly with a bogey on the seventh.

Fellow Briton Eddie Pepperell also made a strong start to the competition as he seeks to secure his Tour card for next season.

The 25-year-old, who needs to retain his current ranking to make the cut, sits one shot off the overnight lead in joint-second position with Finn Mikko Korhonen, America’s David Lipsky and the British pair of Matthew Baldwin and Callum Shinkwin.

Baldwin, 30, needs a top-two finish this week to keep his card and he hit eight birdies in the opening round, although a bogey on the seventh blotted his copybook.

Chris Paisley is among a group of five players a shot further back on six under, along with Swede Jens Fahrbring, who also needs a top-two finish, and Spaniards Alejandro Canizares and Nacho Elvira.

Three-time major winner Padraig Harrington, who chipped in for an eagle on the par-four 15th, will resume on five under, with British players Ben Evans, Ryan Evans, Paul Lawrie and Oliver Fisher also tied on the same score.

Defending champion Andy Sullivan, who last year secured victory by a tournament-record nine shots, is four strokes off the pace on four under.

He praised his supporters for helping him through a bogey-free opening round.

“On the front nine, I felt a little bit down the way I was playing and not really converting and they (the supporters) kept me going for a long time there,” he said.

“Then the back nine I started to play better and give myself more chances.

“It’s down to them that I probably played that little bit better today. If I didn’t have them there, I could have fell into the doldrums after that front nine. Thank ‘Sulli’s Army’ for getting me through.”

Malton’s Simon Dyson enjoyed a promising first day with a round of 67, one shot ahead of Huddersfield’s Chris Hanson, with Harrogate’s John Parry a shot further back