U.S. Open champion Jim Furyk and 1997 British Open winner Justin Leonard paired for a 4-under 68 on Saturday to join Frenchmen Thomas Levet and Raphael Jacquelin, who also combined for a 68, at 7-under-par 209.
Saturday's action was contested in four-balls, or better-ball. Sunday's final round will be played as foursomes, or alternate shot.
The German team of Alex Cejka and Marcel Siem and Sweden's tandem of Fredrik Jacobson and Niclas Fasth posted rounds of 5-under 67 on Saturday and share fourth place at minus-5.
South Africa held a two-shot lead after the first two rounds but wasted little time in extending the margin. Sabbatini rolled home a 10-footer for birdie at the first and the team made it three birdies in a row out of the gate.
'We got off to a great start with three straight birdies and that got us settled down,' said Immelman. 'We played the front nine as good as you can play and it was fantastic to go out there and play so well.'
The duo collected three birdies in a row again, this time from the fifth to pull away from the field.
At the par-5 11th, Sabbatini missed the green short with his second shot but pitched to five feet to set up another birdie. He made it two in a row when he drained a 45-footer from the right side of the green at the par-4 12th.
While Sabbatini was making a mess of the 15th hole, Immelman sank a 20-footer from below the hole for the team's ninth birdie. The team made a solid par after poor drives at the 17th and now have a commanding lead heading into Sunday.
'I would take 18 pars right now and run,' said Sabbatini, who won this year's FBR Capital Open on the PGA Tour. 'I have to say that our 63 is a pretty impressive effort. The course is tough and nothing's easy, even when there is not a breath of wind.'
If South Africa reaches the winner's circle on Sunday, it would mark the second victory for the country in the last three years. Ernie Els and Retief Goosen won a playoff two years ago in Japan and with those two off this week to prepare for next week's Presidents Cup, Immelman and Sabbatini were happy to have the opportunity to represent their country. Especially since both were passed up by International captain Gary Player for the Presidents Cup.
'Missing the team is behind me,' said Immelman. 'So I'm not trying to prove anything to anybody. I'm just here trying to play good golf. It's a great honor to be here and represent the country.'
The Americans mixed five birdies and one bogey on Saturday but are realistic about their chances on Sunday.
'It's never easy making up seven shots. It's possible in alternate-shot format,' said Leonard. 'Neither of us have played great but we haven't played poorly. It's just a matter of hopefully things will kind of fall into place and if we get rolling, see what happens.'
The French pair were alone in second place but a late bogey at the 16th cost them a stroke. Like the Americans, the French know they will have to play very well in the final round if they are to overcome this huge margin.
'It's going to be very difficult for us now,' admitted Jacquelin. 'I feel the South Africans only really need to put the ball on the fairway but we have always known that foursomes is the key to doing well this week and we played pretty well in that format yesterday.'
Spain's Ignacio Garrido and Miguel Angel Jimenez and England's Justin Rose and Paul Casey each combined to shoot 66s on Saturday and are tied for with sixth with Scotland's Alastair Forsyth and 1999 British Open champion Paul Lawrie. The three teams are knotted at 4-under-par 212.
Argentina's combination of Eduardo Romero and Angel Cabrera paired for a 70 and are tied for ninth with the Welsh duo of Ian Woosnam and Bradley Dredge at minus-3.