CENTURION (AFP) - Tillakaratne Dilshan struck a century and Ajantha Mendis grabbed three key wickets as Sri Lanka cruised to a 55-run win over South Africa on Tuesday in the opening Champions Trophy game. Opener Dilshan made 106 as his side reached 319-8 off 50 overs and spinner Mendis sent Graeme Smith, Jacques Kallis and JP Duminy packing as South Africa slumped to 206-7 when rain stopped play with 74 balls outstanding. The Duckworth-Lewis method came into play and Sri Lanka emerged clearcut winners over opponents seeking a first ICC trophy since winning the inaugural Champions Trophy 11 years ago. Smith opted to send Sri Lanka into bat on a run-rich pitch in a gamble that backfired as many of his bowlers revealed rust in their first competitive ODI appearance since losing to Australia last April. Ranked the best ODI team in the world ahead of a two-week tournament second in importance only to the World Cup, South Africa must defeat New Zealand and England at the same venue this week or face a humiliating first-round exit. "We batted very well by doing the basics properly and building partnerships, but we need to brush up on our bowling with which I am about 80 percent happy," said victorious captain Kumar Sangakkara. Smith offered no excuses: "Tillakaratne and Kumar batted superbly and we must improve quickly and hopefully do a lot better. It is a question of getting the basics right." A recent convert from the middle order, Dilshan hit 16 fours and one six in his 106 off 92 balls and a second-wicket partnership with Sangakkara reaped 158 runs on a slow, even-bounce pitch. Dilshan finally departed off the first ball of the 29th over, caught at the boundary by Albie Morkel off the bowling of right-arm speedster Dale Steyn before a near-capacity crowd. It was the third ODI century for the 2009 ICC Cricketer of the Year and Test Player of the Year nominee, whose career-best 137 came against Pakistan in Lahore this year. Wicketkeeper Sangakkara had departed two overs before Dilshan, caught and bowled by JP Duminy for 54 when he played too early on the leg side and got a leading edge. The exploits of Dilshan and Sangakkara followed the early, cheap departure of the grand old man of Sri Lankan cricket, 40-year-old Sanath Jayasuriya, for 10 when trapped leg before by Steyn. Mahela Jayawardene and Thilan Samaraweera proved a further thorn in South African flesh, adding 116 runs off 106 balls for the fourth wicket before they departed from consecutive Wayne Parnell deliveries. Facing a mammoth total, the last thing the Proteas needed was the loss of an early wicket but Hashim Amla was walking back to the pavilion with just nine runs on the board after being bowled by Angelo Mathews. The prize wicket of Smith came in the 15th over as he sought an off break when looking good on 58 and Kallis (41) and Duminy (0) fell to consecutive Mendis balls. South Africa were tottering at 122-4 and any chance of a miraculous recovery vanished as AB de Villiers (24) and wicketkeeper Mark Boucher (26) departed on a dismal day for a team considered title favourites with Australia. SCOREBOARD SRI LANKA T.Dilshan c Morkel b Steyn 106 S.Jayasuriya lbw b Steyn 10 K.Sangakkara c and b Duminy 54 M.Jayawardene c Duminy b Parnell 77 T.Samaraweera c Van der Merwe b Parnell 37 A.Mathews b Steyn 15 T.Kandamby c Duminy b Parnell 6 N.Kulasekara run out 1 M.Muralitharan not out 0 EXTRAS (lb5, w5, nb3) 13 TOTAL (8 wkts, 50 overs) 319 Fall of wickets: 1-16 (Jayasuriya), 2-174 (Sangakkara), 3-181 (Dilshan), 4-297 (Jayawardene), 5-297 (Samaraweera), 6-314 (Kandamby), 7-317 (Kulasekara), 8-319 (Mathews) Did not bat: Lasith Malinga, Ajantha Mendis BOWLING: Steyn 9-2-47-3 (1w) Parnell 10-0-79-3 (1nb, 3w) Kallis 7-0-43-0 Morkel 4-0-39-0 (1nb) Botha 9-0-53-0 (1nb, 1w) Van der Merwe 10-0-42-0 Duminy 1-0-11-1 SOUTH AFRICA G.Smith b Mendis 58 H.Amla b Mathews 2 J.Kallis c Mathews b Mendis 41 AB de Villiers c Jayawardne b Malinga 24 JP Duminy b Mendis 0 M.Boucher lbw b Mathews 26 A.Morkel not out 29 J.Botha c Mathews b Malinga 21 R. van der Merwe not out 3 EXTRAS (w2) 2 TOTAL (7 wkts, 37.4 overs) 206 Fall of wickets: 1-9 (Amla), 2-90 (Smith), 3-113 (Kallis), 4-113 (Duminy), 5-142 (De Villiers), 6-163 (Boucher), 7-198 (Botha) Did not bat: Dale Steyn, Wayne Parnell BOWLING: Malinga 7.4-0-43-2 (1w) Kulasekara 7-0-44-0 Mathews 8-1-43-2 Muralitharan 8-0-46-0 Mendis 7-0-30-3 (1w) Sri Lanka win by 55 runs under Duckworth-Lewis method after rain stopped play Toss: South Africa Umpires: Simon Taufel (AUS) and Ian Gould (ENG) TV umpire: Steve Davis (ENG) Reserve umpire: Tony Hill (NZL) Referee: Jeff Crowe (NZL).