Soprano Renee Fleming smiles after singing the U.S. National Anthem prior to the NFL Super Bowl XLVIII football game between the Denver Broncos and the Seattle Seahawks in East Rutherford, New Jersey, February 2, 2014. (Ray Stubblebine/REUTERS)

For many classical-music fans, Renée Fleming was acting as an ambassador Sunday night. Singing the national anthem at the Super Bowl, she was exposing millions of people to opera.

Classical music is not very secure in its position vis-a-vis the rest of society, and by Sunday night, a lot of us were nervous for her.

Queen Latifah came first, looking and sounding stunning in “America the Beautiful.” Fleming, by contrast, looked like a wedding-cake topper, wearing a black outfit swathed in white — though in close-up she did better, with a dazzling, if strained, smile.

There is no more famous American opera singer today than Fleming, but the Super Bowl represents a different level of celebrity. Although she has sung on national television and has done her share of crossover projects — such as the indie-rock album “Dark Hope” — she had not made this kind of open bid for mass-market appeal (unless you count her singing the top ten list on Letterman last fall).

A big question about her performance was, would she do it straight? Would she sing the anthem how it was written, or would she adopt the embellishments that have become de rigueur at big sporting events? The answer, alas, leaned to the second. Fleming often defaults to a breathy, faux-pop sound, and she started out in her more mannered mode, lingering over the notes and pulling out the line like pizza dough.

But Fleming had to go at least somewhat operatic. And she did sing out, with a full, round sound, a little richer and darker than her norm. One reason it sounded dark was that it was pitched relatively low; she didn’t go above an A. We’ve often heard her sing higher than that on the opera stage, but why take unnecessary chances?

After all, we’re not talking about a major artistic endeavor. What we’re talking about is a major piece of branding — for Fleming, yes, but also for a field eager for any scrap of mainstream attention.

My sense was that Fleming — singing beautifully, her smile growing warmer as she sensed she was pulling it off — succeeded admirably at bringing opera to the table in a way that might get it invited back.

Or not. Reading my Twitter feed after the performance, I came away with the impression that classical music fans thought she did wonderfully, and many others emphatically thought she did not.