Matt Wallace produced a sparkling 63 to set a daunting clubhouse target, before play was suspended on day one of the dual ranking Open de Portugal at Morgado Golf Resort.
The Englishman reeled off ten birdies – including five in a row from the 12th – to get to ten under par and open up a one shot lead over nearest challenger Sebastian Heisele.
Heisele carded an eagle, nine birdies and two bogeys in his opening 64.
American Julian Suri, and Englishmen Paul Maddy and Jamie Rutherford were a further two shots back on six under after posting matching rounds of 67.
Erik Van Rooyen was the best-placed South African, after he opened with a -5 68. Making the most of his opportunity to play in a co-sanctioned Challenge and European Tour event, Van Rooyen made four birdies in five holes around the turn to fly up the leaderboard.
A bogey at the par 3 16th slowed his progress, but it did not keep him off the first page of the leaderboard.
Fellow South Africans Justin Walters and Zander Lombard both carded -3 70s to sit in a share of 18th. Jaco Ahlers is one shot further back.
It was a rough Thursday for Christiaan Bezuidenhout, who struggled to a +4 opening round.
Trevor Fisher Jnr was affected by the delay, and is -1 after 6 holes.
Wallace, who won six Alps Tour events last season to earn his Challenge Tour card, made a strong start on Thursday morning, notching four birdies on the front nine to reach the turn in 32.
The 27-year-old began his back nine in style, making another gain at the long tenth before firing birdies at the 12th, 13th, 14th, 15th and 16th to propel himself to the top of the leaderboard.
Wallace then safely parred his final two holes to head into the clubhouse on ten under.
After his flawless first round, Wallace said: ‘It was a fantastic round really.
‘It wasn’t looking great at the start when the rain came in ten minutes before my tee time. Then it stopped just as we got on to the tee, so that was kind of a good omen.
‘It was the old cliché. I just took one shot at a time and we had a really good day out there.
‘Everything was working well, to be honest. Everything clicked. I made two good par saves on the front nine to keep the momentum going.
‘After that every hole was at least a birdie chance, so it was a really good day.
‘It’s been a continuation of a good start to the season. I’ve enjoyed it, I love coming out here and playing and hopefully we can keep this going for the next three days.’
Play was suspended at 15:10 local time due to the threat of lightning.
