And the box office champion this week is...unknown!

That's right! This weekend tally is too close to call yet. It will be until Monday when we have a clear winner!

LOS ANGELES – Steve Carell and Tina Fey are in a box-office clash with the gods of Mount Olympus.

No. 1 bragging rights for the weekend were too close to call Sunday, with 20th Century Fox estimating a $27.1 million debut for Carell and Fey's comedy "Date Night" and Warner Bros. reporting the action tale "Clash of the Titans" at $26.9 million.

Rankings will be sorted out Monday when studios release final numbers, which can vary by $1 million or more for some films compared with Sunday estimates.

Warner executives said they tracked "Clash of the Titans" as No. 1 for a second straight weekend, with "Date Night" trailing by about $1 million.

"I'm not complaining about it," said Dan Fellman, head of distribution for Warner. "They're certainly entitled to their own projection, and we'll see. Maybe they're right and we're wrong. Monday will tell."

Photo finishes are rare for the No. 1 spot at the box office, where one movie usually is the clear winner.

Weekend projections include fairly hard figures for Friday and Saturday but estimates for how much a movie will take in on Sunday. Studios base those estimates on such factors as how similar movies performed in past weekends.

Studios sometimes grumble that competitors inflate their Sunday numbers to make a debut look stronger.

"You can't do that," said Bert Livingston, a 20th Century Fox distribution executive. "What you do is you look up history, you come up with your best-guess scenario. The number is the number. Whatever it is, if it ends up being No. 1 or 5 or 6, we just estimate our numbers."

Winning the top spot at the box office is a valuable marketing edge, allowing a studio to proclaim its release as the No. 1 movie in advertising through the following weekend.

Even if rankings change on Monday, it's often the Sunday figures that linger in the minds of movie fans, who may not bother to check out the final numbers a day later.

"That's why everyone wants to be No. 1 on Sunday, because with the Internet, by Monday, it's kind of old news," said Paul Dergarabedian, box-office analyst for Hollywood.com.

"Date Night" casts Carell and Fey as a married couple whose attempt to spice up their romantic life leads to misadventure after thugs mistake them for blackmailers.

"Clash of the Titans" features Sam Worthington as a warrior caught in a battle between men and the gods in ancient Greece. The movie raised its 10-day total to $110.5 million.

Running a close No. 3 was DreamWorks Animation's "How to Train Your Dragon," which took in $25.4 million, lifting its 17-day total to $133.9 million.

In narrower release, Vivendi Entertainment's inspirational drama "Letters to God" opened at No. 10 with $1.3 million. The movie centers on a boy who writes letters to God to help cope with his fight against cancer.

Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to Hollywood.com. Final figures will be released Monday.

1. "Date Night," $27.1 million.

2. "Clash of the Titans," $26.9 million.

3. "How to Train Your Dragon," $25.4 million.

4. "Tyler Perry's Why Did I Get Married Too?", $11 million.

5. "The Last Song," $10 million.

6. "Alice in Wonderland," $5.6 million.

7. "Hot Tub Time Machine," $5.4 million.

8. "The Bounty Hunter," $4.3 million.

9. "Diary of a Wimpy Kid," $4.1 million.

10. "Letters to God," $1.3 million.