A slew of major retail tenants have opened, signed leases or are prepared to swap locations along the priciest parts of Fifth Ave. between 42nd and 57th streets, adding new energy and beautifully enhanced storefronts to the costliest and most luxurious retail strip in the world.

At the top of the heap, Bulgari renewed at the southwest corner of W. 57th St. in the Crown Building at a record $5,500 per foot, thus maintaining its ranking as the most expensive crossroads in the world. Some 100,000 square feet of retail at the base of the building, with the address of 730 Fifth, is owned by dealmaker Jeff Sutton and General Growth Properties led by Sandeep Mathrani.

PC enthusiasts hit the Microsoft Store. NY Post Brian Zak

Bulgari is recasting its ground floor spread that will now have 28 feet of frontage on Fifth but its “L”-shaped store will have another 80 feet along W. 57th Street, paving the way for another elegant retailer in between.

“It’s one of the iconic corners in the world,” said Tom Citron, executive managing director of Newmark Grubb Knight Frank.

“If you have a good property and a top-dollar location you can get the customers,” said attorney Brad Kaufman, partner and head of leasing at Pryor Cashman who represents developers and luxury brands.

At the base of the Peninsula Hotel at No. 700 on the southwest corner of W. 55 street, the petite Swarovski and Lindt chocolate shops are being enveloped by the expanding Wempe. Wempe’s Rolex boutique is further south at No. 665 and already split it space with Lindt.

Microsoft opened in the former 22,000-square-foot Fendi spot at No. 677 between E. 53rd and 54th streets, just in time to make its Christmas ad that showed staffers strolling north to sing carols to the rival Apple team at E. 59th Street.

Faith Hope Consolo, Chairman of Douglas Elliman RetailHandout

“The Microsoft store is the new kid in town and customers are lined up outside the door. It’s another tourist mecca,” said Faith Hope Consolo, Chairman of Douglas Elliman Retail.

The St. Regis Hotel’s storefronts, owned by Crown Retail and Vornado Realty Trust. will at some point kiss De Beers and Bottega Veneta goodbye. Swatch-owned Harry Winston will move in while its own townhouse at No. 718 is refreshed and another Swatch brand, likely Breguet, will become its neighbor.

As Gucci moved to its large spread at Trump Tower and is moving its offices Downtown to 195 Broadway, it sold its 115,000 foot building at No. 685 at E. 54th street to Joseph Sitt’s Thor Equities for $460 million. Sitt is renovating the property and bought out 20,000-foot tenant Diesel which  moved to 625 Madison.

Crown, along with Oxford Properties, owns Cartier’s townhouses at No. 653. The jeweler’s space is now undergoing renovations and expanding to 21,500 feet on four levels and a mezzanine.

Cartier is due to move back this year but is likely to retain the 8,000-foot outpost at the GM Building at No. 767 near Apple’s cube.

The office building above Uniqlo at No. 666 may be redeveloped by Kushner Cos. and Vornado Realty Trust.

While the former Juicy Couture at No. 650 at W. 52nd street had a Land’s End pop-up, it will soon have a permanent retailer. Owned by Jeff Sutton and SL Green Realty Corp., no one expects anything less than an exciting and pricey transaction.

When Victoria’s Secret opens its new 64,000-foot flagship in H&M’s former space at No. 640 at W. 51st Street. it should add some lively Angels to the area opposite St. Patrick’s.

While the Real Estate Board of New York’s Fall Retail report found asking rents between 59th and 49th streets averaged $3,397 per foot,  it was an 8.4 percent drop from spring’s $3,683 per foot.  South of  49th, retail rents are lower and average $1,203 per foot.

“We are seeing a push for sites below 49th,” said Laura Pomerantz, vice chairman, Cushman & Wakefield. “If someone is going to spend serious money on a location, Fifth Ave. is the right bet.”

On the northeast corner of E. 46th street the deal by Adidas for 34,000 feet at No. 565 filled in the Build-A-Bear’s workshop which split for a smaller den at the Empire State Building at No. 350.

The new 24,000-square-foot NBA store at 545 Fifth Ave. and 45th Street is a slam dunk.NY Post Brian Zak

“You look at Sephora at No. 597, the NBA, and Adidas; they are great, well-known brands and are taking down significant space and appealing to a wide variety of customers,” said RKF Executive Vice President Jeremy Ezra who represented Adidas. The sport shop also took the 2nd floor space as both L’Oréal and Redken 5th Ave. NYC moved to a cheaper space at No. 404 at 36th street with asking rent of $325 per foot.

The multi-level 25,000-foot NBA store has opened in No. 545 at E. 44th Street.  It left the pricier No. 666 five years ago and then had a svelte store at No. 590.

Gary Barnett of Extell Development is planning a new tower on the Diamond District block midblock between W. 46th and 47th streets. He just secured several Fifth Avenue properties including No. 570 with its prominent address.

The site at No. 520 and W. 43rd is now owned by Ceruzzi Properties and Shanghai’s SMI USA. A 73-story slender tower was planned but permits have been issued.

Sutton and Bobby Cayre’s Aurora Capital own No. 511 on the southeast corner of E. 43rd entirely occupied by IDB Bank. They also own the Skechers at No. 509.

With H&M open at No. 589, its brands & Other Stories and Cos will swap into No. 505 at E. 42nd street.

More changes will come.