Foster, the provisional world No.1 teamed up with Laura Thomas, from Wales, to claim the world matchplay mixed pairs crown from Burnett and Karen Murphy, the new world outdoor singles and triples champion from Sydney, 12-5, 10-6 to add to his world pairs title won the previous day with Alex Marshall.
Burnett and Murphy led 4-1 after three ends but, once Thomas settled down, she played her part in stringing together eight straight shots to ensure that she and Foster led 9-4 with two ends remaining and a treble put the set out of sight with an end to spare. In the second set, Burnett and Murphy counted a treble on the seventh end to lead 6-4 but did not score again.
"Laura was nervous during the opening ends but, once she settled, she got the better of Karen," said Foster. "We played the big bowls when it mattered. Laura has been outstanding in all of our matches and we worked well as a team."
The second round of the singles featured two all-Scottish ties and, in the second, Alex Marshall was brought down to earth just 24 hours after winning a record 19th world title by his Bowls Scotland head coach and No.4 seed David Gourlay.
Playing for a place in the quarter- finals on Friday against the Welshman John Price, Gourlay roared through 9-4, with one end to play, in the first set and 12-1, with three ends remaining, in the second.
Gourlay said: "I put him under a lot of pressure with my first bowl but he got a lot of bad breaks. You've got to play well against him, though, because you can never count him out under any circumstances."
Marshall admitted: "David totally outbowled me. Some days results go for you and some days they don't."
Earlier, Ayr's Stewart Anderson had squeezed past Steven Allan, from Alloa, after a feast of precision bowling. Anderson drew to the jack with the last bowl of the first set, Allan scored doubles on the last two ends of the second and Anderson won a photo-finish with the last bowl of the best-of-three tie-break to edge through 7-6, 3-9, 2-1.
Jonathan Ross, the No.11 seed from Paisley, had earlier brought the first round of the singles to a conclusion by easing past the English qualifier Pat Briscoe 12-6, 7-8, 2-0. He plays England's Mervyn King in his second-round tie tonight, after Foster has taken on Jason Greenslade, last year's beaten finalist from Wales.