Vancsik completed 36 holes at 10-under-par 134. Christian Cevaer carded a 7-under 65 to move into second at minus-9. Santiago Luna, the 1995 champion, is alone in third at 8-under-par 136 after a 67, while David Frost is one stroke further back at minus-7.
Alexander Noren, Mads Vibe-Hastrup and Notah Begay III share fifth at 6-under-par 138.
Vancsik opened his round with a birdie on the par-5 third, then birdied the par-4 fifth for the second straight day to move to minus-6.
After a pair of pars, Vancsik birdied No. 8 at Santo da Serra Golf Club. Around the turn, Vancsik bogeyed the 10th for the second day in a row.
Vancsik bounced right back with an eagle on the par-5 11th to jump to minus-8. The Argentine parred his next three holes.
'I played well for the first nine holes today, then bogeyed the tenth,' Vancsik stated. 'But I chipped in for eagle at the 11th and that brought my confidence back.'
He converted back-to-back birdie efforts from the 15th to move into the lead at minus-10. Vancsik closed with two pars for the 36-hole lead.
'You need (confidence) to play this course because you have to choose the right clubs in some difficult winds and very small greens,' Vancsik explained. 'I don't know what I will do tomorrow and Sunday, but I would like to play the same round for the next two days.'
Cevaer climbed the leaderboard with three birdies on his opening nine holes, the back nine. He made the turn at minus-5.
The Frenchman ran off three straight birdies from the second to jump to minus-8. Cevaer got within one of the lead thanks to a birdie on the sixth.
Cevaer joined Vancsik in the lead when he birdied the eighth for the second day in a row. However, he tripped to his second bogey in two days at the ninth to end one back.
'I just got on the wrong side of the hole on the last and hit a good putt that was unlucky not to go in, but who hasn't had that,' said Cevaer. 'Overall I am very happy. I managed to take my mind off of everything else and focus on my game.'
Jamie Spence matched Frost and Cevaer for low round of the day with a 7-under 65. That moved Spence from a share of 54th into a tie for eighth at 5-under-par 139. Spence was joined there by Fredrik Andersson, Peter Baker, Euan Little, Sam Little, Simon Nash and Oliver Wilson.
First-round leader Ricardo Santos stumbled to a 2-over 74 Friday to fall into a tie for 16th at minus-4.
The cut line fell at 1-over-par 145 with 67 players moving on to the weekend. Among those missing the cut were Alexandre Rocha (146), Mattias Eliasson (147), Maarten Lafeber (148) and 1999 British Open champion Paul Lawrie (148).