Step aside and make way for a real hot awards contender: Sienna Miller is coming on strong as a late-breaking Oscar rival — some gurus even dare to say frontrunner — in the best-actress derby.

Mad awards joy is erupting within Harvey Weinstein's trackside box as his execs and Oscar consultants cheer on a fast-trotting dark horse, "Factory Girl," featuring Sienna as Edie Sedgwick, the debutante party girl who Andy Warhol turned into a pop icon before she descended into lunacy and addiction hell, ultimately dying of a drug overdose in 1971. Harvey and team recently viewed a rough cut of "Factory Girl" and were wowed by what they saw, a nice surprise that arrived late in awards season thanks to production delays caused by hurricane Katrina.

Two of The Envelope's kudos gurus have put Sienna in their top five for best actress — Jeffrey Wells of Hollywood-Elsewhere.com and Peter Travers of Rolling Stone — two guys who know the Oscar beat well. Jeffrey's seen a rough cut, too, and reports, "she kills in it." Based on all of the gushing scuttlebutt I'm hearing, I sure plan to put her in my top 5 as well.

Last year Harvey Weinstein had the Oscar rival who gave the best performance — Felicity Huffman in "Transamerica" — but she lost to the Babe of the Year who gave a rather pedestrian, supporting turn in "Walk the Line." Reese Witherspoon nonetheless won, probably for her past, more-worthy work in "Election" and "Legally Blonde," and, of course, for looking so darn pretty, perky and youthful. Helen Mirren ("The Queen"), Annette Bening ("Running with Scissors"), Judi Dench ("Notes on a Scandal") and Meryl Streep ("The Devil Wears Prada") have good reason to start getting nervous right now about Sienna. Ditto for Penelope Cruz ("Volver"), the only rival babe in the race up to this point.

"Sienna is so amazing in the film that Harvey's planning a big, last-minute academy push," says an aide-de-camp of The Happy Oscar Warrior. "He'll release 'Factory Girl' at the end of December — we don't know the specific day yet — and he's convinced she can win. Sienna's the new 'It Girl' — she's stylish, gorgeous, British and she really did her homework to prepare for the role.

"This really puts Harvey in a terrible spot, though, because he's also planning to push hard for Renee Zellweger in 'Miss Potter,'" adds the source. "Harvey has a special thing for Renee. He adores her. They're very close." Renee has never won best actress — just that supporting trophy for "Cold Mountain," the poor thing — and inside sources say she's good enough, acting-wise, as Peter Rabbit novelist Beatrix Potter to win. In fact, they say this is the best perf of her career. But she's matronly in the movie. She certainly doesn't have The Babe Factor like "Factory's" star and that's what usually wins Oscars for actresses, of course.

Oh, yeah, one last thing: Guy Pearce is said to be aces as Andy Warhol in "Factory Girl," too — good enough for a best actor bid, if he gets lucky. But who needs luck when you've got Harvey on your team, eh? And everybody says Ewan McGregor is charming as Potter's publisher and doomed fiance Norman.

Photos of The Harvey Girls: Drab-looking Renee Zellweger (bottom right) has every good reason to be leery of babe-a-licious Sienna (top), but things could be worse. At least she wasn't forced to look too much like the real Miss Potter (bottom left). (Weinstein Co.)