Atapattu scored an unbeaten hundred (Getty Images).

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Marvan Atapattu's sheet-anchor hundred was the key as Sri Lanka beat Zimbabwe in East London on Saturday to claim the last World Cup semi-final spot at the expense of New Zealand.

Sanath Jayasuriya's former cup winners have earned a last-four tie against holders and competition favourites Australia. But they were deeply indebted to Atapattu (103no), who assessed the limitations of a typically slow Buffalo Park pitch and carried his bat to underpin what turned out to be a winning total of 256 for five.

Zimbabwe's chase began well in their final Super Six match thanks to an up-tempo 43 at the top of the order from Craig Wishart. But the departure of Andy Flower just as he began to look capable of marking his final international appearance with a match-winning effort was a hammer blow - and the eventual 74-run margin of victory slightly flattered the Sri Lankans.

Their total was built around Atapattu, whose unbeaten effort provided the wherewithal for Kumar Sangakkara's late-innings fireworks.

This was an unusual performance with the bat from Sri Lanka, as Atapattu quickly recognised the importance of solid reconnaissance on a surface which lacked the pace to aid fluent strokeplay.

The pioneers of pinch-hitting forsook the approach for which they have become famous and instead relied on conventional batsmanship as Atapattu, Jayasuriya, Avishka Gunawardene (41) and Aravinda de Silva gave Sangakkara the freedom to attack with impunity.

Zimbabwe captain Heath Streak and Andy Blignaut kept a tight line and length with the new ball to stifle Jayasuriya and Atapattu early on.

It took Jayasuriya until the 11th over before he hit his first boundary, a cut off Streak. He followed up in the next over from Blignaut with a neat four off his legs - but that was as good as it got with the bat for the Sri Lanka captain who had come into the game suffering with a broken thumb, tonsillitis and a bruised forearm.

His reward was an uncharacteristically becalmed 22 before Streak got one to dart away off the pitch and snare his opposite number caught behind as he fenced at the ball off the back foot.

The in-form Atapattu had counted two boundaries in one early Blignaut over but otherwise continued to work hard for his runs as Jayasuriya was replaced by Gunawardene, who had been called into the side for Mahela Jayawardene and duly figured in an important second-wicket stand of 83.

There was one slice of luck along the way for Atapattu, who gave half a chance when he drove at a very full delivery and was missed away to his right by wicketkeeper Tatenda Taibu off Travis Friend when he had made 23 in the 16th over.

But he cashed in on his way to a 10th one-day international century which contained seven fours and took him 125 balls.

After Gunawardene had departed to a low return catch by off-spinner Doug Marillier, it was Atapattu and old hand Aravinda who ensured a good platform for the late charge.

Aravinda was well caught by Taibu, standing up to medium-pacer Sean Ervine. But Sangakkara took his cue by blazing 35 from only 25 balls - and the last 10 overs brought Sri Lanka 82 runs as well as two catches for Grant Flower in the offside ring as the batsmen took more and more chances.

Wishart set the tone for a bold reply from the Zimbabwe batsmen when he leant on a cover-drive for four off Chaminda Vaas' only slightly over-pitched second ball of the innings.

He followed up with a back-foot drive straight past Vaas for four two overs later and was ably assisted by Marillier until the all-rounder paid for his ambition and holed out to Jayasuriya at mid-off as he went down the wicket to a slower ball from Pulasthi Gunaratne.

The same bowler also uprooted Friend, who played all round a full-length ball and lost his leg stump, and then Wishart went bowled too when he made room for but missed a back-foot force at Jayasuriya's slow left-arm.

Flower (38), joined by his brother Grant, provided some hope. But when he was fourth out - lbw to Aravinda's innocuous off-spin, even though he appeared to get bat on ball before he was struck on the pad pushing forward - Zimbabwe and New Zealand knew their fate.

Taibu was bowled through the gate by a perfectly pitched Muttiah Muralitharan off-break, and big-hitter Andy Blignaut plonked a Dilhara Fernando full toss straight into Aravinda's hands at cover.

Jayasuriya recalled Vaas, and the left-arm seamer made Sean Ervine pay for hitting across the line to leave Grant Flower much too much to do and Jayasuriya an appropriate opportunity to help hasten the end by taking a cheap three for 30 with his left-arm spin.