EAST MEADOW, New York, June 3 (Reuters) - South Africa defeated Sri Lanka by six wickets in their opening T20 World Cup group match on Monday after dismissing their Asian opponents for their lowest ever score of 77 on a lively drop-in pitch at the temporary Nassau County stadium in Eisenhower Park.

The South Africans also struggled on a pitch cultivated in Adelaide and offering pace, bounce and spin before reaching their target with six wickets to spare and 22 balls remaining.

The pitch offered plenty to all the bowlers with South Africa fast bowler Anrich Nortje taking four wickets for just seven runs. Nortje, 30, has suffered like many pacemen with hip and back injuries but on Monday he was back to his devastating best, bowling with pace and late swing.

"It's a great result for the team because it was a tough wicket," said Nortje who was named Player of the Match. "We didn't know what to expect."

Sri Lanka, who had selected four spinners in contrast to South Africa's four fast bowlers, opted to bat after winning the toss but were immediately floundering as Ottneil Baartman struck with his first ball at a World Cup. Nortje also captured a wicket in his opening over, dismissing Kamindu Mendis for 11.

Left-arm spinner Keshav Maharaj struck twice with wickets off successive deliveries when seasoned all-rounder Angelo Mathews went briefly on the counter-attack with two sixes before he was caught for 16 to give Nortje his final wicket.

South Africa also struggled...