And, in the best of all possible ways, it’s a daringly old-fashioned performance—the kind we feel exceptionally lucky to witness nowadays. From his first strutting entrance as Ionesco’s 400-year-old King, Mr. Rush is not only in relaxed and riveting command of the stage; he is saying—while not exactly saying—“Watch this!”

He brings to this potentially difficult role the nearly lost art and irresistible joy of performing—and makes Ionesco wonderfully accessible in the exhilarating process.

Ionesco said of his so-called theater of the absurd—The Chairs (1952) and Rhinoceros (1959) are among his other classics—that he was influenced by the Marx brothers, Grand Guignol puppet shows and Kafka. Mr. Rush gives us the disturbing and farcical essence of all three—topping them up nicely with an expert combination of music hall, circus and Shakespeare. That his Everyman King Berenger finds a tragic Shakespearean depth of human wreckage amid the hilarity is among the miracles of a masterly performance.

The demanding role was famously originated (in its English version) by Alec Guinness, but I cannot imagine even that great actor equaling Mr. Rush’s achievement. The introverted Guinness was slyly comic, whereas Mr. Rush’s huge and grotesque interpretation is exactly in tune with what Ionesco termed the “violently comic, violently dramatic.” In the exaggerated theater of the absurd, nothing is ever quite real—except the show.

Academy Award winner Susan Sarandon (Queen Marguerite) and Lauren Ambrose (playing Marie, the other Queen) are among the strong ensemble in Neil Armfield’s splendid, near childlike production. But all eyes are forgivably drawn to Mr. Rush’s bravura King. The Australian actor (also an Academy Award winner) is a born clown. He has the face and mask of one. Peeking out from his gold paper crown, his hair is revealed as startled tufts of red—until it turns white. (Shakespeare’s clowns were traditionally red-headed.)

Mr. Rush is also a gifted mime. He falls beautifully onstage (like no one else since the 73-year-old Ralph Richardson in Harold Pinter’s No Man’s Land). It is a slow crumpling that his decrepit, rubbery King does, like a puppet whose wires have been cut: The landing is soft; the rise speedy and limber—until the next fall.

You never know what Mr. Rush might do next. (But then, nor does the King.) After all, Exit the King takes place in a world—Ionesco’s as well as ours—where the abnormal has become the new normal. The star actor thrives on the unpredictable, dangerous edge of theater. His energy is mercurial, electric and gleeful; his despotic King ultimately pathetic and extraordinarily humane.

And the play itself? Oh, that! In hifalutin terms, Ionesco’s renowned “anti-play” at the Ethel Barrymore is theatrically akin to a Cubist painting. In plainer terms, Exit the King is about insane self-delusion and nothing less than the futility of life. It’s about death.

But don’t let that discourage you in the least. The absurdist play has stood the test of time, and Mr. Rush’s 400-year-old King is one for the ages.

Fortunately, what Ms. Reza has done with God of Carnage, at the Bernard B. Jacobs Theatre on Broadway, is to write a welcome boulevard comedy polished to a high gloss by her frequent translator, Christopher Hampton. After the soupy pretentiousness of her last outing here, The Spanish Play, Ms. Reza has returned to the successful formula of Art: a small group of politely civilized people meet, talk and, one way or another, end up trying to kill each other.

God of Carnage concerns two sets of middle-class parents who meet to resolve a violent fight that took place between their young sons in the schoolyard—and their lives unravel accordingly. Thankfully, Ms. Reza makes only fleeting allusion to the tragedy of civil war in Darfur, while her boisterous 85-minute light comedy proves a triumph of escalating farce.

The marvelously paced production confirms—if confirmation is needed—the Brit Matthew Warchus as a leading director on both sides of the Atlantic. Last season, he breathed glorious new life into what was assumed to be a dead horse with his revival of Boeing-Boeing. (He also directed the original production of Art, among other Reza plays.) But Mr. Warchus’ supreme ensemble of actors in God of Carnage is a particular delight.

The director never relies on purely comic performers for the laughter—but on fine actors who proceed to the ridiculously farcical via a considered seriousness and politesse. The terrific James Gandolfini and Marcia Gay Harden are one hilarious couple; the equally smashing pairing of Jeff Daniels and Hope Davis are the other. The quiet riot Ms. Davis—to whom I declared undying love and adoration over a decade ago—has returned to the New York stage at last, and her astonishing projectile vomit over the entire proceedings must be seen to be believed.

jheilpern@observer.com