The actress "snuck back into his dressing room," a source tells PEOPLE

By Mark Gray
Updated September 20, 2014 12:40 PM
Credit: Kevin Mazur/WireImage; Mark Davis/Getty

Sin City offered up throngs of fans for Chris Martin‘s Friday performance at the iHeartRadio music festival.

But one very special Coldplay fan watched the Las Vegas show from the sidelines: Martin’s new lady love, Jennifer Lawrence.

Following a few quiet date nights at Martin’s Malibu home and a romantic dinner on Sept. 8, the actress stepped out to support the musician for a more public – and louder – appearance.

“She was off to the side of the stage when he performed,” a source tells PEOPLE.

Lawrence, who was seen backstage, showed off her midriff in a studded black crop top, matching denim bottoms and stilettos.

And Martin seemed to take notice.

“I’ve never seen such a well-dressed audience,” he said.

The Hunger Games star watched as Coldplay performed a 30-minute set that saw them spray star-shaped confetti over the sold out crowd.

“After his set, she snuck back into his dressing room,” the source adds.

But prior to the performance, Lawrence was treated to a much more intimate show.

“She was watching him during his closed rehearsal and was singing along,” says the source.

Jennifer Lawrence, from Red Carpet Newbie to Bona Fide Star

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