The Waratahs must beat the defending champion Blues at Eden Park for the first time since 2009, then hope Moana Pasifika fall to the Hurricanes later on Saturday to secure a miraculous berth in the play-offs.
And the Tahs will need to notch a famous victory at New Zealand rugby's traditional graveyard for rival teams without inspirational halfback and captain Jake Gordon.
With Gordon out injured, coach Dan McKellar has opted for a new halves combination with flyhalf Jack Bowen promoted to start alongside new No.9 Teddy Wilson at one of rugby's great cauldrons.
Playing possibly his last game for NSW with his future beyond this season uncertain, Sinclair is demanding the Waratahs' pack steps up on Saturday afternoon to make life easier for the rookie pairing.
"It's obviously a different beast over here, Eden Park, against the Blues but you've got to throw them in some time," Sinclair said at Friday's captain's run.
"You've just got to throw them in and see how we go, and our boys are really excited.
"Bowie's been great. He's still got Tane (Edmed) on the bench, you've got Lawson (Creighton) there, (Andrew) Kellaway. It helps having that experience around them as well.
"They'll be fine. As long as the pack can get on the front foot and make life a bit easier for those guys, I think we'll get the result.
"You've got to take it to them over here at Eden Park, especially against the Blues. They're a quality outfit, so it's exciting and the boys and me are up for the challenge."
Sinclair is well aware the Tahs haven't won at Eden Park in 16 years, but feels being underdogs has its advantages.
"We've just got to go out there and play," the lock said.
"There's no pressure, no expectation for us to win, so we can really just focus on ourselves and not focus on any of the outside noise."
If the Waratahs win, they'll face an anxious wait of around three hours to see if the sixth-placed Hurricanes topple the Moana, who are coming off an 85-7 loss to the Chiefs.
"Obviously you can't control that, unfortunately," Sinclair said.
"We'll do as much as we can to get through and see what happens, I guess."
Should they progress, the Waratahs will play the Chiefs in Hamilton in another do-or-die away match in the first week of the finals next weekend.
The Chiefs clinched top spot, the minor premiership and home-ground advantage for however long they last in the finals with a 41-21 win over the Highlanders on Friday night.
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