A half-century from Faf du Plessis led South Africa to a series-clinching victory in the third one-dayer against Sri Lanka on Tuesday. Chasing 267 to win, the home team were 179 for five after 34 overs when rain ended play. According to Duckworth-Lewis calculations South Africa were four runs ahead of Sri Lanka, giving them an unassailable 3-0 lead in the five-match series. The 27-year-old Du Plessis lifted South Africa from 52 for three with 72 off 74 balls, the highest of his three half-centuries, before he became the second batsman to be run out in the innings as he failed to beat a throw by Angelo Mathews. Captain A.B. de Villiers then took over with an aggressive 39 not out off 36 deliveries. Challenging score Earlier, fast bowler Lasith Malinga put Sri Lanka on top by clean bowling Graeme Smith for two and Colin Ingram for 13. Sri Lanka totalled 266 for nine after winning the toss. Their top four all scored more than 30 but only opener Upul Tharanga (58) managed a half-century. Nuwan Kulasekara provided some impetus in the closing overs with 40 off 38 balls. The fourth match is in Kimberley tomorrow. Fact Box Sri Lanka 266 all out South Africa -    G. Smith b Malinga 2 -    A. Petersen lbw b Dilshan 17 -    C. Ingram b Malinga 13 -    F. du Plessis run out (Mathews) 72 -    J. Duminy run out (N. Kulasekera) 25 -    A de Villiers not out 39 -    A. Morkel not out 7 -    Extras (lb2, w2) 4 -    Total (5 wkts, 34 overs) 179 -    Fall of wickets: 1-14 (Smith), 2-29 (Ingram), 3-52 (Petersen), 4-113 (Duminy), 5-147 (Du Plessis) -    Bowling: Malinga 5-1-20-2 (2w), N. Kulasekera 6-0-31-0, Prasad 5-0-38-0, Herath 6-0-24-0, Dilshan 5-0-22-1, K. Kulasekera 3-0-21-0, Mathews 4-0-21-0 -    Did not bat: R. Peterson, D. Steyn, M. Morkel, L. Tsotsobe -    Result: South Africa won by 4 runs (Duckworth/Lewis method) -    Man of the match: Faf du Plessis (RSA) -    Series: South Africa lead the five-match series 3-0 -    Toss: Sri Lanka -    Umpires: Johan Cloete (RSA), Nigel Llong (ENG) -    TV umpire: Billy Doctrove (WIS) -    Match referee: Jeff Crowe (NZL) Remaining matches: Jan 20, Fourth ODI, Kimberley (day/night) 22, Fifth ODI, Johannesburg (day).