Macy’s delivered a July fireworks show for investors yesterday – with a little help from Madonna.

The nation’s biggest department store reported a better-than- expected 7.3-percent increase in July same-store sales, or sales at stores open at least a year.

While other retailers, including rival JC Penney, were singing the back-to-school blues with sluggish monthly sales reports, Macy’s CEO Terry Lundgren said the season is “off to a great start.”

Lundgren cited the “phenomenal launch” of the new “Material Girl” fashion line, designed by Madonna and her 13-year-old daughter, Lourdes. Aimed at teenage girls, the 1980s-inspired line will include clothing, shoes, handbags and jewelry.

On Tuesday, Macy’s launched the collection at the company’s flagship store on Herald Square with a performance by pop star Taylor Momsen, who drew throngs of girls dressed up like Madonna. Macy’s shares yesterday rose 34 cents, or 1.8 percent, to $19.78.

istockanalyst