Liam Neeson fended off aliens, gnomes, and big mommas, as the thriller Unknown topped the charts Friday with $6.7 million, according to early estimates. That trails the opening-day tally of Neeson’s 2009 hit Taken, which earned $9.4 million its first day. Regardless, with a modest budget of $31 million, Warner Bros. has to be pleased with Unknown‘s initial result. Yet will the movie be able to claim victory over the extended Presidents’ Day weekend? That’s tough to say this early, but Unknown will likely be battling with Gnomeo & Juliet for first place, even though the latter placed fifth on Friday. Gnomeo, Disney’s animated musical starring garden gnomes, dropped only 30 percent for $4.3 million. It should perform even better today and Sunday, and with kids out of school on Monday, the G-rated family film could skyrocket into first place for the holiday weekend. At the moment, Gnomeo is on pace for a four-day grab of around $27 million, while Unknown is headed for about $26 million. But these projections could fluctuate depending on how things play out today and tomorrow.

What does look certain, however, is that the new sci-fi action film I Am Number Four will fall short of expectations. The $50 million film, a DreamWorks project that’s being released via Disney’s Touchstone Pictures, grossed $6.2 million on Friday and is on pace to finish the four-day weekend with around $22 million. Many box-office prognosticators pegged Number Four to open with at least $30 million (I went with $29 million), but unless the PG-13 movie receives a major boost today, it won’t finish anywhere near that mark. Third place went to the Adam Sandler romantic-comedy holdover Just Go With It, which slipped 45 percent for $5.2 million. And Big Mommas: Like Father, Like Son debuted in fourth place with $4.8 million. The Martin Lawrence comedy should finish the long weekend with about $19 million.

As for audience satisfaction, all three new releases — Unknown, I Am Number Four, and Big Mommas — received sturdy “B+” grades from CinemaScore moviegoers. Check back here tomorrow for another update, and on Monday for the complete box office report.

1. Unknown — $6.7 mil

2. I Am Number Four — $6.2 mil

3. Just Go With It — $5.2 mil

4. Big Mommas: Like Father, Like Son — $4.8 mil

5. Gnomeo & Juliet — $4.3 mil