Defending champions the Bulls, the Sharks and the Waratahs are vying for two playoff spots this weekend as Super 15 Rugby organisers have had to juggle flight schedules due to Chile's volcano ash cloud.

It's a potential winner takes all for the Bulls and Sharks in a compelling South African derby in Pretoria on Sunday, especially if the Waratahs win their all Australian final round match against the Brumbies in Sydney.

The Bulls, tournament winners in three of the past four seasons, and the Sharks are just one point ahead of the Waratahs, who can clinch a playoff place if they defeat the Brumbies tomorrow night.

Looking at the matches this week:

Tonight at 7.35 the Blues take on the Highlanders and at 9.40pm the Rebels will meet the Force.

Hurricanes will play Crusaders at 7.35pm tomorrow, but before that match, Reds face Chiefs at 5.30pm and at 9.40pm Waratahs take on Brumbies in Sydney.

Two matches will be played Sunday morning.

At 3.05am Sharks will face Bulls and at 5.10am Cheetahs will play Stormers.

Story by: Shalvin Deo
Source: Super rugby.com