LOS ANGELES (Reuters) - Khloe Kardashian's first outing as the new co-host of "The X Factor" helped boost the show's audience by 30 percent, yet the reality star got mixed reviews for a nipple-baring debut that made headlines - but many TV critics found awkward.

Kardashian, 28, best known for starring with socialite sisters Kim and Kourtney in "Keeping Up with the Kardashians," shocked some viewers by wearing a sheer purple blouse without a bra on Wednesday's first live episode of the TV singing contest.

"I think the air conditioning is on high tonight. It's very distracting," judge and producer Simon Cowell quipped on the show, apparently referring to the glimpses of nipple.

But Kardashian was less impressive in her hosting duties.

The Washington Post said Kardashian "came across like the novice she is, shouting her lines despite the mic clutched in her hand and making awkward small talk with contestants and judge and executive producer Simon Cowell."

Nevertheless, Kardashian brought more eyeballs to the show. Some 7.4 million viewers watched "The X Factor" on Fox television, according to early ratings data, up some 30 percent from last week's 5.7 million and a 13 percent increase in the 18-49 age group most coveted by advertisers.

Kardashian was Cowell's personal pick for the job as part of his efforts to revamp the singing contest after a disappointing first season. But the reality star's lack of experience had already raised eyebrows, and "X Factor" has often drawn a smaller audience than last year.

Cowell told reporters earlier this week that Kardashian "wants to prove (to) anyone who doubted her that she's capable of doing the job ... she really has got a fun personality."

The New York Daily News called Kardashian a "surprisingly good host," while The Hollywood Reporter said "both Kardashian and (co-host Mario) Lopez seemed at ease in their new roles."

The Hollywood Gossip website, however, said Kardashian was "every bit as boring and awkward as we imagined she would be."

"The X Factor" is broadcast on Fox, a unit of News Corp.