It's knockout rugby in this weekend's Super 14 action. A defeat for any of the top teams chasing semifinal places will either eliminate them completely or seriously hobble their chance of making it to the play-offs.

And matches don't get any bigger than at Newlands and Loftus this weekend, where the Stormers meet the Crusaders and the Bulls play the Sharks. Three of the top four sides are in action at these two venues and, by the completion of the round, the standings could have a very different look.

The Reds, in fourth place, travel to the sixth-placed Brumbies in another crucial match tomorrow.

But the most critical match from a South African perspective is between the Stormers and Crusaders, because the home side cannot afford a loss.

The Bulls, by contrast, could drop a game and still remain in top position when the dust settles - thanks to the five-point cushion they hold at the top of the standings. But with matches against the Crusaders and Stormers to follow, dropping points to the ninth-placed Sharks on home soil is simply not an option.

The Stormers and Crusaders are second and third on the standings, with 34 points each, and defeat will almost certainly lead to the loser dropping out of the top four with two rounds to go.

The Stormers have the added incentive of becoming the first South African side in Super rugby history to record a clean sweep over New Zealand teams.

They've so far beaten the Highlanders (33-0) and Hurricanes (37-13) at Newlands, and recorded victories over the Blues (33-21) and Chiefs (49-15) on tour.

The Crusaders have a good record in Cape Town, having won three of the six Super rugby matches staged at Newlands. The last time they were here they beat the Stormers 22-0 on their way to the title in 2008.

Crusaders captain Richie McCaw admitted to The Times this week that this Stormers side is about the best he's seen, t hough far from invincible - but they certainly have their best chance in years to topple the Crusaders, who are not at their all-time best.

"We've struggled to put an 80-minute performance together this season, but we're still in the running and have done enough in a lot of the games," McCaw said. "It's been frustrating, but having that feeling and still being in with a shot at the title is a good thing."

The Bulls, on 39 points, are always happiest at Loftus and could all but cement a play-off berth if they secure a full five-point haul against the Sharks this weekend.

They're aiming to stretch their Loftus winning run to 17 matches and, despite the Sharks' recent resurgence, it's hard to bet against the Bulls extending that record.

Bakkies Botha returns to the second row after a long Achilles injury lay-off. He will no doubt be a little ring-rusty but he will be fresh.

The Sharks will not make it easy for the Bulls because they harbour microscopic play-off hopes as well, and understand that only a full five-point haul will be enough to keep those hopes alive.

The Cheetahs host the Blues in Bloemfontein, wanting to secure their first win over the New Zealanders, and the Lions meet the Western Force at Ellis Park on Saturday.