IT’s no mystery how actress Kate Danson got a plum part on “CSI.”

Her dad, Ted Danson is the star of the show – and sources say that the former “Cheers” bar­tender twisted some arms at CBS to get his precious little girl the role.

“Kate didn’t have a lot of experience,” said a source. “Mostly bit parts. If it wasn’t for her famous father, she never would have gotten it.

“Ted really went to the wall to make sure his daughter got on the show.

“Yes, it’s Hollywood nepotism and Ted knows it.

“But, as he put it, ‘I’m the star of ‘CSI’ now and if I want my daughter on the show, she’s on the show!’”

Kate, 33, is Danson’s daughter with second wife Casey Coates. He’s now married to third wife actress Mary Steenburgen.

Kate guest starred on the April 3 episode as lawyer Jill McDermott and there’s talk that it could be a recurring role – a really big break.

“I play a lawyer who knows she’s in the right and the CSI team has done something wrong,” Kate said.

“So I come pretty hard at my dad and dig into him, which was a lot of fun to play.

“I was really fortunate to get to work with him on ‘CSI.’ It was so much fun. We never worked together like that. We did a short film together but nothing professional until now, so it was really great going head to head with him.”

Not everyone’s happy for Kate, though, says the source.

“A lot of people on the show were griping that Ted pulled some major strings for his daughter and a lot more accomplished actresses were passed over. But Ted’s attitude is, ‘Oh, well, those are the breaks.”