Fast bowler Kagiso Rabada produced the best bowling performance of the tournament to date as South Africa beat three-time former champion Australia by 80 runs in the second semi-final of the ICC U19 Cricket World Cup 2014 in front of Star Sports cameras at the Dubai International Cricket Stadium on Wednesday.

Rabada, who came into the match with seven wickets, returned figures of 8.2-0-25-6 as Australia, chasing 231 for victory, lost its last seven wickets for 54 runs in about 14 overs to be bowled out for 150 in 42.2 overs.

Rabada dismissed the top three batsmen to leave Australia reeling at 33 for three, and then returned to rip the heart out of the Australia middle and lower middle-order with some very fast, aggressive and accurate bowling.

The only Australia batsman to bat with some confidence was Jake Doran who scored 36 while captain Alex Gregory contributed 31. The two batsmen put on 66 runs for the fourth wicket in about 22 overs. The partnership ended when Rabada brought off a smart catch at mid-off to dismiss Gregory.

Both the batsmen fell to Corbin Bosch who finished with impressive figures of two for 25.

Wednesday's result means both the finalists from the 2012, Australia and India, will now feature in the play-offs, while Saturday's final will be between two-time former champion Pakistan and South Africa, which has previously reached the final in 2002 and 2008. The final will be broadcast live by Star Sports and will start at 1200 local time.

Earlier, South Africa survived a middle-order collapse to post a competitive total on the board.

Wicketkeeper-opener Clyde Fortuin hit a classy 74 and captain Aiden Markram scored a polished 45 as the two batsmen put on 105 runs in less than 21 overs for the first wicket. This was their first century partnership of the tournament and it couldn't have come at a better time.

Fortuin, who later excelled behind the stumps by bringing off three smart catches, hit eight fours in a 92-ball innings. Markram, who fell to a spectacular catch by Guy Walker in the gully, hit four fours in a 63-ball 45.

Fortuin, after the departure of Markram, added 45 runs for the second wicket with Kirwin Christoffels (20) to take the score to 150 for one in 30 overs before South Africa lost the plot and stuttered to 230 for nine, thanks to Yaseen Valli's 36-ball 31 with three fours at number-six.

Australia bowlers bowled much better in the middle of the innings and were all well rewarded. Matthew Short snapped up two 14, Billy Stanlake claimed two for 36 while Ben Ashkenazi picked up two for 37.

Rabada, 18-year-old from Johannesburg, later said: "My plan was to stick to line and length, and bowl fast. I'm glad that this paid off.

"It is important that we keep our feet on the ground and stay relaxed and composed for the final."

Markram praised his side for putting up an impressive show, when he said: "It's an amazing feeling to be in the final. We are delighted but we'll move forward with our feet on the ground and we will take on the next challenge that lies ahead.

"It is amazing to have Rabada in your armoury. We can call on him whenever, wherever and I believe he was due for this performance. I am extremely happy for him that it paid off."

Looking ahead to the final, Markram said: "Pakistan has always managed to put out a good side at any level of cricket, so we're definitely not going to take them for granted. I think it is of massive importance to come here with calm heads and to just enjoy playing in the final."

A disappointed Gregrory said: "We're a little bit disappointed but South Africa played very well. They got off to a very good start and carried that momentum right through the game.

"Rabada bowled very well, bowled with good speed and energy. It was very hard to bat against him.

"We're now hoping to win our game against England and claim third place in the tournament."