The Blues qualified for the Super Rugby Semi-finals when they beat the Waratahs 26-13 in Auckland at Eden Park on Friday.
The Blues will however have to wait until tomorrow to find out if they will travel to Cape Town or Brisbane for their Semi-final.
If the Sharks beat the Crusaders the Blues will travel to Brisbane but if the Crusaders beat the Sharks the Blues will travel to Cape Town to face the Stormers.
The Blues had a shaky start as they allowed the Waratahs to take an early lead but they fought back and took control of the game in the second half.
Both teams scored two tries each but the Waratahs discipline cost them as Lachie Munro kicked three penalties and Luke McAlister kicked another which kept the Waratahs from gaining any momentum.
Ali Williams, battling to regain his All Blacks place after almost two years on the sideline with injury, scored a 62nd-minute try which took the match beyond reach of the Waratahs.
The Blues' semifinal opponent will be decided by the outcome of Saturday's second elimination match at Nelson between the Crusaders and Durban-based Sharks.
The Waratahs suffered a continuation of the injury problems which have plagued their season, losing both starting locks Kane Douglas and Sitaleki Timani to injuries before bowing to the Blues in a battle of attrition.
The match was riddled with errors from both sides and at times degenerated into an inconclusive kicking duel before the Blues composed themselves to maintain a small advantage through the second half.
The Waratahs started more strongly, exploring a yielding Blues defense in the first 20 minutes during which the Blues missed nine first tackles.
That allowed the Waratahs to almost camp in their half and led to the first try of the match, to Waratahs center Tom Carter after 17 minutes.
There was a noticeable gap in the Blues' defense around flyhalf where Stephen Brett had an unsteady beginning.
Kurtley Beale, playing at flyhalf on attack and fullback on defense, explored the inside channel and managed on several occasions to work the ball behind the Blues backline.
A stretched defense finally snapped to give up Carter's try just beyond the quarter hour.
Replacement hooker John Ulugia made good ground in midfield for the Waratahs and Beale was quick to spot an advantage of numbers wide on the left-hand side.
Ryan Cross committed defenders and Carter drove over the line through the ineffective tackles on No. 8 Peter Saili and center Luke McAlister.
Beale made a try-saving tackle on Blues fullback Jared Payne in the 22nd after McAlister initiated a counterattack, chip-kicking for the wing of All Blacks star Joe Rokocoko.
Rokocoko claimed McAlister's kick on the fly, linked with Payne and the fullback had only Beale to beat when the Wallabies utility brought him down in a copybook tackle.
The Blues retained possession when Williams won the ball from a lineout. They moved the ball quickly through the backline and McAlister passed to Munro, who hurdled his marker to score.
The Waratahs reclaimed the lead with a Beale penalty after 30 minutes but the Blues led 10-8 after a 33rd-minute penalty to Munro - who took over the kicking from McAlister who converted his try.
A further penalty to Munro in the 35th gave the Blues a 13-8 lead after a first half in which the lead changed hands three times.
Munro's third penalty in the 55th gave the Blues an eight-point lead and Williams' try, evoking memories of his best form, made the lead 23-8 and effectively ended the Waratahs' season.
It was typical of the spirit shown by the Waratahs in a difficult year that it still hit back with a 74th-minute try to fullback Lachlan Turner.
But McAlister had the final say with a long-range penalty in the 77th which made the final margin emphatic.
Final Score Blues 26 Waratahs 13
Tries - L Munro, A Williams
Pen - L Munro 3, L McAlister
Con - L McAlister, L Munro
Tries - T Carter, L Turner
Pen - K Beale
Referee: Chris Pollock
AR 1: Stuart Dickinson
AR 2: Glen Jackson
TMO: Vinny Munro
Blues: 15 Jared Payne, 14 Joe Rokocoko, 13 Benson Stanley, 12 Luke McAlister, 11 Lachie Munro, 10 Stephen Brett, 9 Alby Mathewson, 8 Peter Saili, 7 Luke Braid, 6 Jerome Kaino, 5 Ali Williams, 4 Anthony Boric, 3 John Afoa, 2 Keven Mealamu (c), 1 Charlie Faumuina.
Replacements: 16 Tom McCartney, 17 Tevita Mailau, 18 Chris Lowrey, 19 Daniel Braid, 20 Chris Smylie, 21 Winston Stanley, 22 Sherwin Stowers.
Waratahs : 15. Lachie Turner , 14. Atieli Pakalani , 13. Ryan Cross , 12. Tom Carter , 11. Sosene Anesi , 10. Kurtley Beale , 9. Josh Holmes , 8. Dave Dennis , 7. Phil Waugh [c] , 6. Dean Mumm , 5. Sitaleki Timani , 4. Kane Douglas , 3. Paddy Ryan , 2. John Ulugia , 1. Benn Robinson
Reserves: 16. Elvis Taione , 17. Jeremy Tilse , 18. Pat O'Connor , 19. Chris Alcock , 20. Hugh Perrett , 21. Brendan McKibbin , 22. Bernard Foley