Spain and New Zealand were together in fourth place after 9-under 63s, while Ireland, South Africa and host Japan finished knotted in sixth at minus-eight. Denmark and England shared ninth place with 7-under 65s.
The dynamic American duo of Tiger Woods and David Duval, ranked first and third in the world, respectively, began the defense of their title in somewhat shaky fashion with a 6-under 66. They were alongside six other teams including Fiji, featuring 2000 Masters champion Vijay Singh, and Australia, with young guns Aaron Baddeley and Adam Scott.
Dean Robertson, who replaced the injured Volvo PGA champion Andrew Oldcorn for Scotland, collected seven birdies in the four-ball format, while teammate Andrew Coltart recorded three. The Scots had a chance to take sole possession of the lead but Robertson missed a six-foot putt for eagle at the par-5 18th.
'It would have been a lovely way to finish a lovely day, but unfortunately it wasn't,' said Robertson, who birdied all four par-5s at The Taiheiyo Club's Gotemba Course in Japan.
The towering Robert Karlsson, who was paired with British Open runner-up Niclas Fasth, eagled the sixth and 18th holes to fuel Sweden's climb to the top.
'We started out slow, but finally got rolling from the sixth hole,' Karlsson said. 'Niclas made a couple of real nice birdies and it was a lot of fun out there.'
Karlsson's eagle at the sixth was set up by a 250-yard 2-iron to three feet. He made a three at the last by rolling in a 20-footer.
Canadians Mike Weir and Ian Leggatt made a tremendous surge on the way to the clubhouse with a back-nine 29. Weir, winner of the Tour Championship in a playoff earlier this month, produced six of his team's 10 birdies on Thursday.
Read 'Weir Understands History of 'World Cup''
Sergio Garcia, who is coming off his best season after winning twice on the PGA Tour in the U.S. and adding a third career victory on the European Tour, racked up eight birdies, including four in a row to close his round with fellow Spaniard Miguel Angel Jimenez.
The dream pairing for the U.S. didn't click in the first round.
Woods dumped his approach to the 15th in a bunker and barely kept his next shot from the sand on the green. Although Duval birdied the hole to negate Woods' troubles, the reigning British Open champ took a practice putt on the 16th green and was assessed a two-stroke penalty.
The penalty was enforced on the 17th, wiping away Duval's birdie there and making the best score on the hole Woods' par.
'I wasn't swinging well and I definitely wasn't putting well. Add those two things together, and you're not going to get low scores,' said Woods, who won five times on the PGA Tour this season but had stretches of inconsistency. 'If I would have made a couple of more putts, we could have shot a little lower.'
The U.S. is seeking its third straight World Cup title and its 24th overall. Before successfully joining forces with Duval in Argentina last year, Woods teamed up with Mark O'Meara to win the event in Malaysia in 1999.
The 24 teams in the field will play an alternate-shot format in Friday's second round.
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