Theo Wargo / NBC 1 / 18
Theo Wargo / NBC 1 / 18

Oh, Betty! January Jones turned up the heat as she left her undergarments at home during an appearance on "The Tonight Show" with Jimmy Fallon on Friday.

PHOTOS: Stars without underwear

The "Mad Men" actress, 36, wore a revealing, yet classy, black jumpsuit for the visit with matching heels. The plunging neckline ensemble showed off major skin with cut-out detail placed strategically down her leg. To top it off, Jones kept her makeup simple with a touch of light blue color.

PHOTOS: January with a mullet -- and other hilarious #TBT pics

Earlier in the day, Jones stepped up her fashion game once again in an '80s-inspired look. The "X-Men" star was photographed outside her hotel in NYC wearing an edgy white blazer with a black t-shirt and J Brand "Genevieve" jeans. She completed the look with a bold red lip and bee-hive hairstyle.

Jones and her fellow AMC costars are currently in NYC for the show's upfront presentation. On Thursday, she shared a stunning selfie in her hotel room. "Objects in a @tomford mirror are prettier than they appear. Thanks @hungvanngo @rebekahforecast," she wrote.

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