Rihanna's Diamonds World Tour has had its first cancellation ... the pop star has postponed her March 10 Boston date because she has laryngitis, a Live Nation rep has said in a statement:

    "Unfortunately, following her sold-out concert on Friday, Rihanna has contracted laryngitis and per doctor's instruction is unable to perform this evening."

The tour kicked off in upstate New York March 8, with a performance in Buffalo. Ri Tweeted after the gig, "#BUFFALO I will never forget how you made me feel tonight!!! Thank you from the bottom of my heart!! #1Love always"

Rihanna is expected to return to the stage March 12 in Baltimore.