A total of 11 players are just one shot back at minus-4. Heading that group is Adam Scott, who collected his sixth tour win earlier this year at the Qatar Masters.
Scott was joined at 4 under by Paul Sheehan, Jason Knutzon, Unho Park, Greg Chalmers, Robert-Jan Derksen, Mark Foster, James Kamte, Taichiro Kiyota, Rahil Gangjee and local favorite Jeev Milkha Singh.
There are 10 more players tied at 3-under-par 69 at DLF Golf and Country Club.
Vancsik opened with three straight pars. After faltering to a bogey on the fourth, the Argentine birdied the fifth and sixth.
However, he slipped back to even-par as he bogeyed the par-3 eighth, then made the turn at minus-2 thanks to an eagle on the par-5 ninth.
Vancsik followed that with a birdie on No. 10 and moved to 4 under with a birdie on the 12th. The 2007 Madeira Islands Open winner collected his last birdie on the par-4 15th.
'I have been working hard since the end of the season,' admitted Vancsik. 'I feel very well, though I didn't have too many chances at birdie today.'
Khan started on the back nine and posted his first birdie on the 11th. After four straight pars, he birdied 16 and 18 to turn in minus-3.
The Indian parred the first six holes on the front nine, then chipped in for birdie on the seventh and closed with a 12-foot birdie putt on the ninth to earn a share of the lead.
'My round was pretty solid. My putting was very good, I took only 24 putts,' said Khan. 'Because of the speed of the greens, I was a little wary of them, but the day turned out really well.'
Singh had taken over the lead briefly when he drained the sixth birdie of his round at the 15th. However, he bogeyed the next two holes to finish at minus-4.
Likewise, Scott's fifth birdie of the day on the par-5 14th gave him a piece of the lead at 5 under. He stumbled to a double-bogey on the par-3 16th, but recovered one stroke with a birdie on the 17th.
'I'm very pleased with how I played today,' Scott stated. 'I had one poor shot, but I don't think it really spoiled the round. I was pleased with everything to be honest.'
Among those tied for 14th at minus-3 are Arjun Atwal, Soren Hansen and Jose Manuel Lara.
Vijay Singh is one of 12 players at 2-under 70, while defending champion Anton Haig is one shot further back at minus-1.