Vancsik, the 2007 Madeira Islands Open champion, finished two rounds at Royal Park I Roveri at 9-under 133 for a one-stroke edge over first-round leader Gareth Maybin (70) of Northern Ireland.
Finland's Roope Kakko (64), Iceland's Birgir Hafthorsson (65) and England's Anthony Wall (67) share third place at 7-under 135, while local favorite and 2006 Italian Open champion Francesco Molinari (69) leads a large group at 5-under 137.
John Daly, continuing his nomadic trek of the international tours, shot a second-consecutive 69 to share 16th place at 4-under 138.
'Yesterday could have been really low,' said Daly, 'but today could have been really high.'
Maybin, who held a three-shot lead overnight, managed only two birdies and one bogey in the second round, opening the door to the field. He labored throughout the round.
'I had to work really hard ' too hard ' and I'll do a bit of work on the range to sort my driving out,' said Maybin, a rookie. 'Usually anybody who finishes well is going to have one of those days, so hopefully that's mine out of the way.'
Vancsik, meanwhile, built on his nearly-flawless tournament so far with a steady 65 that included six birdies and 12 pars. He has only bogeyed one of his 36 holes thus far.
'I hit my driver very well,' said Vancsik. 'On this golf course, it is very important to hit fairways.'
Vancsik got off to a good start with a birdie at No. 1, but didn't begin to make his run until the middle holes. He collected five birdies in a six-hole stretch from No. 6 ' then finished the round with seven consecutive pars.
He nearly holed a chip-shot for eagle on 11.
Vancsik, 32, could use a good finish this week to wash away the bad taste of a thus-far disappointing season.
A 10th-place finish in his home country at the Argentine Masters ' not a European Tour stop ' has been overshadowed by a slew of middling performances. He hasn't finished better than a tie for 42nd place in any of his other nine worldwide starts.
Vancsik agreed that Friday marked his best round of the season.
'I think so. Every tee shot I just tried to put it in the fairway,' he said.
Vancsik has struggled with a shoulder injury, but insisted that it was no longer an issue.
'It's not an excuse,' he said. 'I feel perfect.'
The cut line fell at even-par 142 with 70 players making it to the weekend. European Ryder Cup captain Colin Montgomerie (144) and 2008 Italian Open champion Hennie Otto (72) were among the players who missed the cut.