Three’s a crowd for “American Pie” cutie Tara Reid and her new beau David Schwimmer — she’s fending off her ex-fiance Carson Daly’s desperate attempt to woo her back!

Tara dumped MTV hunk Carson earlier this summer after catching him cheating on her, while “Friends” star David recently got the heave-ho from longtime galpal Mili Avital.

But Tara, 26, and 35-year-old David hooked up in Las Vegas at the November 15 opening of the new Palms Casino Resort — and they’ve been inseparable ever since.

“Tara and David were both on the rebound from bitter breakups,” said an insider.

“Now Carson can’t seem to get the message that she’s not going to come crawling back to him.

“He’s been besieging Tara with phone calls in recent weeks with an eye toward reconciliation. He also showed up at Tara’s celeb-studded birthday bash at the club Eugene in Manhattan, spending all evening bending her ear in a private booth.

“But Tara was just being kind. Now she’s fed up with the frantic messages from Carson. Tara is never coming back.

“When she caught Carson cheating on her at the same time they were making wedding plans, she was devastated.

“She just couldn’t come to terms with all the terrible things she believes he’s done — cheating with a succession of models and strippers and then lying to her about it.”

Now the “Josie and the Pussycats” star has filled the empty place in her heart with new beau David.

The night after the Palms opening, eyewitnesses say the new lovebirds kissed, cooed and cuddled in a VIP booth during a Macy Gray concert at the nightclub Rain before showing up arm-in-arm at the Lennox Lewis-Hasim Rahman heavyweight fight on November 17.

Then instead of flying back to New York, where she lives, Tara followed her new object of affection back to Los Angeles.

“Tara’s been staying at David’s new $5.5 million luxury home in the Hancock Park area of L.A. and they’ve been hitting Hollywood hotspots like The Latin Lounge,” a friend of the couple disclosed.

Another source added: “Tara’s main residence has been in New York, but she’s spending her free time in Los Angeles with David.

“Carson broke Tara’s heart and Mili broke David’s. And in Las Vegas, David and Tara found each other.

“How serious their relationship is, it’s too soon to tell. But they’ve given each other a new lease on life.”