For the next week, Sydney theatre audiences can see perhaps the finest American play of the past decade and one of the greatest American plays of the past century in repertory.

It’s a rare and distinguished double: Pulitzer Prize winners, both, prosecuting relationships and mortality with devastating and lasting impact. August: Osage County and Our Town — existential masterpieces modern and timeless — are theatre at its most potent.

Cate Blanchett and Andrew Upton, partners in life and artistic directorship, have delivered sparkle and substance to a Sydney Theatre Company season that has proudly wrapped itself in the stars and stripes. Of all the Americana featured this year, these two plays will be the standouts. The best kind of cultural imperialism.

Sydney Theatre at Walsh Bay suffocates the audience in the familial melodrama of August. There’s little more that can be said: Tracy Letts’ jet-black dramedy of a dysfunctional family reunion has been lavished with glowing reviews and industry awards since its 2007 debut (Crikey‘s theatre critic said it’s the “finest modern play, and production, I’ve ever seen”).

While the Melbourne Theatre Company mounted its own production last year, the STC has transported the original Chicago production — cast and all; the famed Steppenwolf ensemble — across the Pacific. The authenticity is palpable; less theatre than breathtaking voyeurism — and you can’t look away for the more than three-hour duration. It’s the most naturalistic performance I’ve seen on a stage. And among the most affecting.

A short stroll under the Harbour Bridge, to the Drama Theatre bunker of the Sydney Opera House, is a play featured on most lists of the greatest written. Thornton Wilder’s Our Town — a character-driven slice of America’s small-town south in the early 1900s — is the essence of life itself: amiably meandering for the most part before, when you least expect it, smacking you in the head and reminding you what the point is. Written in 1938, it has inspired American Beauty and so many other life-affirming tales. None enrich the soul quite like this.

In a preview performance I attended last week, several people walked out after two sparsely staged (mimed, even) and perfectly quaint acts. Nothing happens, they mumbled. Which was exactly Thornton’s point. The third act explodes with regret and redemption to leave the audience reeling. Those that stayed won’t soon forget it.

Both plays plead with audiences not to take life for granted; to appreciate what you have before its gone. To miss either of them would be utter betrayal.

The details: August: Osage County closes at the Sydney Theatre on Saturday — beg, borrow or steal a ticket. Our Town plays the Drama Theatre at the Sydney Opera House until October 30. Tickets for both shows on the STC website.