Fred Hersch is playing six nights of piano duets at the Jazz Standard in New York City this week, pairing off with a different pianist each night, and Tuesday’s opening set was a marvel, further evidence that Hersch, not quite 52, is one of the two or three most harmonically imaginative jazz pianists on the scene and keeps carving new pathways—more intricate and probing, but no less swaying or lyrical.

His duo-partner last night was a former student of his, Ethan Iverson, 34, best known as the pianist in The Bad Plus but deserving acclaim as much, much more. I wrote recently about Iverson’s duet performance at the Blue Note with the bassist Charlie Haden—a startling, near-perfect mesh, despite quite different sensibilities—and his interplay with Hersch was no less eye-opening.

It was, first of all, a pleasure to watch two musicians in such total command of their instruments. The duet may be the most challenging format: both players are upfront constantly, yet they can’t go their own ways; each must remain unceasingly alert and responsive to what the other is doing or might do next; one lax moment can bring the edifice tumbling down. In this sense, a piano duet is tougher still. At least with a piano and bass, or piano and saxophone, it’s pretty clear who’s going to be playing what part. With two pianos, both can play melody, harmony, counterpoint, and who-knows-what all at once; the task is to sort it all out—in the moment (this is pretty much unrehearsed improv)—without sounding cautious on the one hand or like a train wreck on the other.

Hersch and Iverson know their 88 keys as intimately and completely as anyone playing them. A few years ago, Hersch recorded an album of Monk covers (called Thelonious), which may be the most dangerous thing a jazz pianist can do. Try to play Monk as Monk did, and you inevitably sound like a second-rate imitator. Try to do something different, and you court the risk of not sounding sufficiently Monkish. Hersch accomplished the amazing feat of not sounding at all like Monk—at least not literally—but nonetheless capturing Monk’s spirit. Iverson, it seems, has absorbed the entire tradition of jazz piano (and a good bit of 20th-century classical, as well), and knows how to unleash just the right bits of it at just the right moment with just the right touch. The Bad Plus is a fun band; in a way, they’ve created their own genre (and their new album, Prog, is in some ways their best); but Iverson can stretch way beyond what they do, and I hope some record label soon lets him.

Last night’s early set began with an Iverson original, followed by a staggered-rhythm rendition of Sonny Rollins’ “Doxy” (which Iverson played in the saucy, slow manner of a Hampton Hawes blues), and moved on to a Monk, a Hersch tune based on “Ornithology,” and wound up with an encore of “Star Eyes,” with Iverson pounding the bass intro from the Charlie Parker version. Throughout, the two traded fours, eights, and numbers incalculable to the mere onlooker, seamlessly, clairvoyantly, and joyously.

About two-thirds into the hour-long set, Iverson said to the audience that musicians often play badly in front of their teachers, then added, “I’ve been pretty relieved by what’s happened in this set.” Rightly so.

Tonight, Hersch plays duets with Brad Mehldau, tomorrow with Kenny Barron, Friday with Jason Moran, Saturday with Geoff Keezer, and Sunday with Art Lande.