The Australian pair of Adam Scott and Craig Parry combined for a 5-under 67 and is alone in fourth place at 17-under-par 127.
The American team of Phil Mickelson and David Toms, ranked first in the competition, shot a 5-under 67 to share 13th place with Myanmar and Argentina at 12-under-par 132, seven shots out of first.
'We're a good ways back, but we're not an uncatchable ways back,' said Mickelson, who is ranked second in the world. 'Tomorrow will be a big day for us. We need to shoot 13, 14-under-par and we'll be able to make up some good ground.'
Singh and Chand combined for six birdies and a bogey on the front nine in this alternate-shot format, but made their move to the top of the leaderboard on the back nine at the Nicklaus Course at Vista Vallarta Golf Club.
They tallied birdies at 11 and 12 to get near the top spot but it was their play down the stretch that moved them to first. Singh and Chand birdied the last three holes thanks to Singh's sharp iron game and Chand's putting.
Singh, the 2000 Masters champion, knocked the team's approach to eight feet at No. 16 to set up birdie. Singh then hit his tee shot to 10 feet at the par-3 17th for another birdie and Chand holed a five-footer at the last to grab the one-shot lead.
Chand, who plays mostly on the Japanese PGA Tour, may have surprised some in the golf world with his play through the first two rounds but not himself nor his partner.
'I try to play better than Vijay every time I play with him, which I have for the last two days,' said Chand. 'I'm a good putter.'
'I think his golf game is a lot better than people think it is,' said Singh, who at seventh in the world is the third-highest ranked player in the event behind the Americans. 'I think he's going to be a good player in the future.
'Last year was the first time we played together and the first time I represented Fiji in golf as a professional. This is a big thing for us and we would definitely like to win it.'
South Africa also birdied the last three holes to polish off an 8-under 64 and get within one shot of the lead, a position that is familiar to the country. In 2001, Ernie Els and Retief Goosen led South Africa to a playoff victory in the WGC-EMC World Cup.
'I'm sure because Ernie and Retief aren't here, people were expecting us not to do so well,' Sabbatini said. 'Hey, we are not the top-10 players in the world here, but Tim and I have been playing golf together since we were eight years old. We know each other's game.'
'We felt we had a good chance this week,' said Clark. 'We've played a lot of this sort of format as juniors and have both been playing well this week. The scores show that'
Canada was flawless on Friday with five birdies and no bogeys. On a day to go low at Vista Vallarta, team Canada made only one birdie on the second nine.
England's team of Justin Rose and Paul Casey shot a 63 in the second round and is tied with three other teams in fifth place. Those teams are the Japanese duo of Shigeki Maruyama and Toshi Izawa (64) joined Scotland's Paul Lawrie and Alastair Forsyth (65) and Korea's K.J. Choi and S.K. Ho (67). The group is tied at 16-under-par 128.
Saturday's play returns to the four-ball or best ball format and Sunday's final round will be in foursomes or alternate shot.
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