Tillakaratne Dilshan's superb century and Ajantha Mendis's fiery three wicket haul helped Sri Lanka register a 55-run victory over South Africa via Duckworth Lewis method in the rain-affected first match of the ICC Champions Trophy in Centurion. Sri Lanka started their campaign on a perfect note as they first amassed 319 for eight in 50 overs after being invited to bat first and then put up a disciplined bowling performance to prevent South Africa from upstaging them.Chasing 320 to win, skipper Graeme Smith hit a defiant 58 en route his 81-run first wicket stand with Jacques Kallis (41) to raise hope of a successful run chase but Mendis soon picked up three crucial wickets to spoil South Africa's dream. Rain also added to South Africa's woes when play was called off because of torrential rain with Albie Morkel (29) and Roelof van der Merwe (3) at crease and scoreboard reading 206 for seven in 37.4 overs at Supersports park on Monday.Earlier, Sri Lanka produced a brilliant batting display with Dilshan leading the peck with a blistering 92-ball 106, followed by Kumar Sangakkara (54), Mehala Jayawardene (77) and Thilan Samaraweera (37).Chasing a daunting total, South Africa lost opener Hasim Amla (2) in the third over when he dragged Angelo Mathews onto his stumps but Smith (58) and Kallis (41) made sure that they don't lose any more wicket. After a few silent overs, the duo stepped on the gas and sent the bowlers for a leather hunt as South Africa surpassed the 50 mark in 9.2 overs. Smith looked more dangerous and in the 10th over he hit Nuwan Kulasekara for two fours and a six on way to his 39th ODI fifty in 40 balls in the 14th over.Soon Mendis was introduced into the attack and the Lankan spinner struck in his first ball rocking Smith's woods. With spinners Muttiah Muralitharan and Mendis bowling in tandem, runs dried up as Kallis and newman Ab De Villiers (24) picked up ones and twos to keep the scoreboard ticking.However, twin strike by Mendis in the 21st over, removing Kallis and JP Duminy (0) in successive deliveries, pushed the Proteas on the back foot as they looked down the barrel at 113 for four in 21.4 overs. Soon Lasith Malinga accounted for De Villiers as the right-hander miscued one to give an easy catch to Jayawardene and after sometime Mark Boucher (26) and Johan Botha (21) also followed him to the hut. Albie Morkel (29) tried his hand but couldn't do much as the match slipped out of their fingers.Earlier, Sri Lanka were off to a reasonable start with Dilshan hitting the third ball of the innings for a boundary at cover. Sanath Jayasuriya (10) soon joined the party and sent Wayne Parnell across the cover boundary twice. But pacer Dale Steyn spoiled the party, trapping Jayasuriya infront of the wicket as Sri Lanka were reduced to 16 for one in 2.2 overs. Dilshan kept attacking the bowlers and along with skipper Sangakkara forged a 158-run stand for the first wicket before the latter was sent packing by JP Duminy in the 28th over.Six balls later, Steyn had Dilshan caught at third man by Albie Morkel as his second wicket to reduce Sri Lanka to 181 for two in 29.1 overs. Dilshan's innings was studded with 16 fours and one six. Jayawardene and Samaraweera then joined hands and helped the side surpass the 200 mark in 34 overs and then exploded in the end to swell the total as Sri Lanka crossed the 300-mark hurdle in the 47th over.For South Africa, Wayne Parnell and Dale Steyn bagged three wickets each.