Though he grew up near Tokyo, Hiroyuki "Zama" Tanaka never had the rigorous decade-long apprenticeship there that is the famed rite of passage for Japanese sushi chefs. Slinging burgers and pizza at Camp Zama, the American Army base in Kanagawa Prefecture that inspired his nickname, was about the limit of his culinary experience in his homeland.

Rittenhouse Square, it turns out, is actually where Zama found his sushi muse and training. So when you see the tousle-haired chef these days working his art behind the smooth maple sushi bar of his stellar new self-named restaurant - slicing jewel-box-like bowls of chirashi, lightly torching buttery pads of albacore, or brilliantly reinventing the California roll without rice or fake crab - know that it all began just a block away nearly two decades ago.

At the once-great Genji (now the uninspired Kin Gyo), the revered sushi elders put the 20-year-old Temple University exchange student through his paces, teaching him to scale, gut, and fillet for months before they let him actually work with the fish.

"They didn't even let me touch the rice," says Zama, who first had to understand the vagaries of different crops and seasons, the right way to rinse, the perfect kombu-and-vinegar seasoning and paddle work to lend each grain the proper tang and texture to help each morsel of raw fish sing.

A quick learner and personable counter man, Zama soon became a rising star, running Genji's boutique counter at the Ritz-Carlton, pushing the sushi cart (blowtorch in hand) at short-lived Fish on Main in Manayunk, and, finally, feeding the fusion fans by conveyor belt at Pod for much of the last decade, though some of those big rolls too often wore flash over function.

It is only fitting, then, that the now 38-year-old should come into his maturity as a sushi chef back in the old hood with his own restaurant, Zama, just a block north of Rittenhouse Square. Not only is his fish work there the best of his career - with a sharper focus on ingredients and elegant composition - but the restaurant as a whole is the most impressive all-around Japanese destination to open in this town since Morimoto.

The quality of the fish and its preparation is simply pristine, especially in the ever-changing market specials. Ribbons of parrot fish came dusted with yuzu shavings that lent its flukelike delicate mildness a citrus sparkle. Golden-eye snapper (kinmedai), edged with the electric pink lacework of its skin, was amazingly tender and fresh. The baby yellowtail (kampachi) melted like fish velvet. The butterflied orange clam, glistening over a pad of perfectly toothy rice, had the clam's distinctively fleshy snap and briny savor. A live scallop, meanwhile, so feisty its shell snipped at the chef's fingers until it met the fateful blade, arrived in thicker-than-usual sashimi discs that slipped across my tongue with an intense tidal rush of sea and sweetness.

The sashimi purist should be thrilled even with a more involved creation such as the precious chirashi lunch, a naturalistic bouquet of raw fish - creamy orange uni, rich salmon topped with ikura jewels, deep purple tuna, and white snapper - artfully arrayed over a bed of rice seasoned with ginger and marinated mushrooms, and a noodlelike shred of sheer egg crepe.

But Zama also manages to produce some signature maki rolls with something elusive - creativity that bows to the ingredients, not simply the distracting crutch of spattered sweet and spicy sauces. His tuna California roll is a masterpiece of contained and harmonious flavors, a core of sweet lump crab (not that fake "krab") with creamy avocado, tingly masago mayo, and snappy cucumber wrapped in a meaty roll of purple tuna. The surf-and-turf brings shrimp tempura embraced in pounded sheets of tender Kobe beef that get lightly torched and spiced with togarashi pepper with a minty yuzu "chimichurri" that brings the roll alive. The "bronzizzle," meanwhile, is a more soft-spoken ode to branzino, a rarely used-as-sushi fish that sparks against crispy shallots and a hot sesame yuzu-soy drizzle.

To be sure, Zama is not perfect yet. The drinks list is decent, but an active work in progress, a little slow to acquire Japanese craft brews such as Hitachino Nest and Coedo - though they're due to arrive soon, along with some coveted Japanese whiskeys (such as Hibiki) and a larger sake selection.

The decor is also a mixed bag depending upon where in the 80-seat room you sit. I loved the smoothly sanded, unvarnished touch of the Lancaster maple slab at the sushi bar, and also the night-sky tranquillity of the sand garden-like tracings of a koi pond across the vaulted rear ceiling of the former Loie space. But the room is also outfitted with so many vertical wooden slats, one can get dizzy when the Tenryo Koshu junmai daigingyo sake really starts flowing, and those booths suddenly begin to feel disconcertingly like oversize cribs, or the Zama zoo.

It's a small gripe, though, for a restaurant that does so many other things right. The service has been superb, as our two young servers - Erin and Georgianna - struck the perfect combination of authoritative in-depth knowledge and chatty charm, unpretentiously parsing details of the fish and sake, and seamlessly orchestrating the multicourse meals.

Even the cooked side of the menu, a weakness at many Japanese restaurants, delivered some inspired delights. The amazingly tender short rib, braised in Kirin Ichiban beer and served zebra-striped with miso mustard over a nest of crispy noodles, was devoured in a blur of tugging chopsticks by my piranhalike dining companions. A vivid green dusting of spicy miso salt elevated an already stellar piece of Angus N.Y. strip to memorable. The tempura of Chilean sea bass morsels and cauliflower tossed in spicy mayo is an addictive welcome twist on that tired old rock shrimp fusion standard.

Zama handles two classics familiar to Morimoto fans with great aplomb - an irresistible miso-marinated black cod that avoids treacly sweetness (Bounty paper towels are the secret), and the table-made tofu whose unbelievably silky and naturally sweet curd pairs with an umami-bomb of dashi-splashed mushrooms.

There were, of course, a few uninspired moments. The seared skate special was way oversalted. The usually pounded tonkatsu chop of Berkshire pork was left far too thick. Among the otherwise knockout rolls, I wished there was more scallion crunch in the negi-toro roll, as well as a more obvious lobster punch in the low-impact "lobster wasabi." At $17, that lobster roll wasn't cheap - like all the fish here.

But for the most part, Zama delivered stellar quality upgrades to some standards worth the fee - like the sustainably raised Kindai bluefin tuna, the gorgeous brick-orange coho salmon (ever-so-slightly cured around the edges), and a boat-shucked uni packed in seawater that was a shade saltier than the typical urchin, but melted in slow motion on the tongue from saline to sweet.

Speaking of sweets, Zama has a few unexpected moves here, too, from the Mont Blanc cake wound in a hive of piped chestnut cream to the Satsumaimo S'more pie that layers sweet potato over spiced cake beneath a house-made marshmallow. Even more startling were the house ice creams, vivid with honey, ribboned with toothsomely sweet red beans, or tinted to a stunning charcoal hue with black sesame, which tasted something like frozen halavah.

What a nice surprise to find a Japanese restaurant that pays attention to the dessert course. But by that time, it was already clear that Zama - both the chef and the restaurant - is turning out to be something special.

Next week, restaurant critic Craig LaBan reviews Green Eggs Cafe in South Philadelphia. Contact him at 215-854-2682 or claban@phillynews.com.