CAPE TOWN (AFP) - Mitchell Johnson hit an 86-ball century for Australia before South Africa completed an innings and 20-run win on the fourth day of the third Test at Newlands Sunday. Johnson and Andrew McDonald (68) shared an Australian record seventh wicket stand of 163 to delay South Africa's consolation victory. Australia won the series 2-1. Left-arm spinner Paul Harris took six for 127 and fast bowler Dale Steyn three for 96. South Africa were on course for a crushing victory when Australia lost their sixth wicket at 218, still 224 short of avoiding an innings defeat.But McDonald and Johnson, voted man of the series, went for their shots and thrashed a tiring bowling attack. They put on 163 in 122 minutes off 161 balls to break the Australian seventh wicket record against South Africa of 160 by Richie Benaud and Graham McKenzie in 1963/64. The stand was ended when McDonald was caught at silly mid-off off Harris. Johnson was on 95 while Peter Siddle was out first ball, also caught at silly mid-off. Johnson, who was stranded on 96 not out in the first Test in Johannesburg, faced Steyn, who placed eight fielders on the boundary in an invitation to Johnson to take a single and expose new batsman Bryce McGain. But Johnson pulled the second ball for six to raise a maiden Test century.In the same over Johnson called for a suicidal second run and McGain was run out at the bowler's end.Johnson finished on 123 not out off 103 balls with 11 fours and five sixes. Only 40 runs were scored during the morning for the loss of Simon Katich's wicket but three wickets fell between lunch and tea before McDonald and Johnson came together. South Africa had to wait 98 minutes before Harris had Katich caught at mid-off after Katich and Mike Hussey dug in with cautious batting, adding just 36 runs from the start of play. Katich was out for 54, adding 10 runs in 60 balls before playing a loose drive. He could have been out without adding to his overnight 44 when Harris put down a straightforward chance at gully off Steyn in the ninth over of the morning.Hussey was caught at gully off Steyn four overs after lunch for 39 and Brad Haddin became Harris' third victim when he holed out to mid-on. Australian vice-captain Michael Clarke made a fighting 47 before he was bowled off an inside edge by Steyn, armed with the second new ball, shortly before tea. Clarke earlier was given out by umpire Steve Bucknor after he appeared to be caught behind off Jacques Kallis when he had made two. But Clarke immediately asked for a referral and survived when replays showed his bat hit his pad. It was the fourth successive time a decision by Bucknor, standing in his last Test match before retirement, was overturned on referral. SCOREBOARD AUSTRALIA, 1st innings: 209 (S.Katich 55) SOUTH AFRICA, 1st innings: 651 (A.B. De Villiers 163, A. Prince 150, J.Kallis 102, A. Morkel 58) AUSTRALIA, 2nd innings: (overnight 102-2) P. Hughes c Kallis b Harris 32 S. Katich c Duminy b Harris 54 R. Ponting c Boucher b Steyn 12 M. Hussey c Duminy b Steyn 39 M. Clarke b Steyn 47 B. Haddin c Duminy b Harris 18 A. McDonald c De Villiers b Harris 68 M. Johnson not out 123 P. Siddle c De Villiers b Harris 0 B. McGain run out (Engelbrecht) 0 B. Hilfenhaus c Prince b Harris 12 EXTRAS: (b8, lb2, nb5, w2) 17 TOTAL: (all out, 121.5 overs) 422 Fall of wickets: 1-57 (Hughes), 2-76 (Ponting), 3-138 (Katich), 4-146 (Hussey), 5-191 (Haddin), 6-218 (Clarke), 7-381 (McDonald), 8-381 (Siddle), 9-387 (McGain), 10-422 (Hilfenhaus) BOWLING: Steyn 27-5-96-3 (nb1, w1) Ntini 19-6-66-0 (w1) Morkel 20-1-88-0 (nb2) Harris 42.5-9-127-6 (nb1) Kallis 10-4-21-0 (w1) Duminy 3-1-14-0. Result: South Africa won by an innings and 20 runs. Series: Australia won 2-1. Man of the match: Paul Harris (RSA) Man of the series: Mitchell Johnson (AUS) Toss: Australia Umpires: Asad Rauf (PAK) and Steve Bucknor (WIS) TV umpire: Billy Bowden (NZL) Match referee: Jeff Crowe (NZL)