Brisbane suffered an unexpected loss at Newcastle 44-18.
Vuna ran riot after the break to run in three more tries with Isaac De Gois added an eighth score for the Knights.
Brisbane’s only riposte came in the shape of a 61st minute score from Israel Folau.
South Sydney’s final’s hopes received a crushing blow when they were demolished 54-18 by a resurgent Penrith.
But Michael Gordon bagged a second half brace including a last minute try to confirm Penrith’s dominance.
Manly held on to record a vital 19-16 win over the New Zealand Warriors.
Canterbury triumphed narrowly over North Queensland 22-20 in a meaningless game in Townsville.
Tries from the Williams’ pairing Ty (2) and John (1) gave the home side the edge at the break 14-6.
Melbourne heaped yet more misery on Cronulla, despatching them 24-4 at AAMI Park.
A Cameron Smith try and conversion was all that separated the sides at half time with Melbourne leading 6-0.
Canberra continued their remarkably good record against St George by thrashing the NRL table-toppers 32-16.
Brett Morris’ try gave the Dragons a narrow 4-0 lead at half time after a nervy opening 40 minutes.
Wests Tigers survived a nerve-jangling end to their clash with Parramatta to hang on 20-18.
Ryan crossed again after the break for the Tigers as did powerful youngster Andrew Fifita to open up a healthier 20-6 lead.
Luke Burt could have sent the game into overtime but unbelievably he missed his penalty attempt and Parra were sunk.
Gold Coast looking to be hitting form into the finals series if their 23-14 win over Sydney is anything to go by.
The Roosters hit back after the break with a try from winger Sean Kenny-Dowall but Bodene Thompson’s try and a second to Toopi opened up a healthy advantage.
Scott Prince’s field goal put the Titans out of sight and despite a late try to Anthony Minichiello, it was a case of too little too late for the Roosters.