The Waratahs slumped to a 34-28 loss against the Blues at Eden Park in Auckland on Friday but maintain a slim chance of reaching the finals after earning a consolation bonus point.

The Waratahs were outscored five tries to four as the Blues staunchly defended their lead, bouncing back whenever the Sydneysiders looked like reeling them in.

The visitors entered the match level with the Brumbies on 39 points at the top of the Australian conference and desperate to claw ahead of their rivals.

The Australian conference winner will make the playoffs but the season will be over for the runner-up, with final placings decided when the Brumbies play the Western Force on Saturday.

The loss means the Waratah's, the 2014 champions, need the Force to spring a massive upset against the Brumbies.

"You never know, stranger things have happened... we'll wait and see," captain Michael Hooper said.

The result means the Blues, who are rebuilding under coach Tana Umaga, have won 14 of their last 16 matches against Australian Super Rugby sides at Eden Park.

They also defeated the Brumbies last week, meaning the bottom placed New Zealand side has defeated the top two Australian sides in the past fortnight.

Wet conditions hampered the Waratahs' preferred running rugby style and they initially struggled with turnovers and knock-ons but built pressure through the forwards.

They were rewarded with a penalty try in the 22 minutes after their dominant scrum drew a string of infringement from the Blues.

But the Aucklanders hit back four minutes later when Patrick Tuipulotu latched onto Tevita Li's pass and crashed over in the corner.

The Blues then took a 12-7 lead with a penalty try of their own when the Tahs collapsed a driving maul as the Blues were bearing down on the line and poised to score.

Referee Mike Fraser awarded the third penalty try of the match early in the second half, this time to the Waratahs after more scrum woes for the Blues.

But they were able to hit back again almost immediately when Piers Francis went on a jinking run and weaved past five tacklers before touching down.

A penalty extended the Blues' lead to 22-14 and they looked like running away with the game before Israel Folau burst into open space for the Waratahs third try.

The tit-for-tat scoring continued with Malani Nanai adding a fourth for the Blues, then Angus Ta'avao doing the same for the Waratahs.

George Moala finally sealed it for the Blues in the 76th minute after the Waratahs' defence was stretched by a lineout drive.

SCORERS

Blues - Tries: Patrick Tuipulotu, penalty try, Piers Francis, Melani Nanai, George Moala. Conversions: Piers Francis (3). Penalties: Francis.

Waratahs - Tries: Penalty tries (2), Israel Folau, Angus Ta'avao. Conversion: Bernard Foley (4).

Referee: Mike Fraser (NZL) - supersport