Chopra, the winner of the PGA Tour's Ginn sur Mer Classic in late October in Florida, had a 12-under 204 total on the Huntingdale course. He had eight birdies and needed only 23 putts.
'I've been coming here for years, it's like a second home,' said Chopra, whose only bogey Saturday was on the par-3 12th. 'I haven't had one of those rounds for a while where I got everything going, and today was the day.'
Barnes also shot a 65, and Baddeley had a 69.
Australia's Rod Pampling (67) was 9 under, and second-round leader Robert Allenby (73) was 8 under along with fellow Australian Stuart Appleby (68) and England's Richard Finch. Allenby won the 2004 and 2005 tournaments.
Rory McIlroy, the 18-year-old Northern Ireland player who turned pro in September after finishing as low amateur in the British Open, was 7 under after a 70.
Chopra said the conditions were ideal for scoring.
'The wind was down. I needed to score,' Chopra said. 'My plan was to get a good start. I managed to do that, scrambled a couple and then got on a roll.'
The event is sanctioned by the European and Australasian tours.