There’s no stopping Avatar‘s “shock-and-awe” performance at the box office. For the fourth weekend in a row, James Cameron’s sci-fi blockbuster was No. 1 with $48.5 million, according to early estimates by Box Office. While the majority of holdovers plunged about 50 percent this weekend, Avatar slipped only 29 percent while crossing a series of milestones in the process. First, Avatar passed Transformers: Revenge of the Fallen to become 2009’s highest grossing film. The 3-D epic also leaped over Spider-Man and Pirates of the Caribbean: Dead Man’s Chest to become America’s seventh-highest grosser, and by the end of next weekend, Avatar is likely to jump four more spots to become No. 3 on the all-time list.

Perhaps most impressive of all, however, is that Avatar posted by far the top fourth weekend on tally. The next best performance was another Cameron movie, Titanic, which earned $28.7 million during its fourth weekend. The burning question now is whether Avatar will have enough steam in the tank to knock Titanic off its perch as the domestic and worldwide box-office king. Titanic grossed $600.8 million domestically and $1.8 billion globally, while Avatar is currently sitting with $429 million domestically and $1.3 billion worldwide. Hold on to your hats, folks.

In second place (yes, people were seeing other movies too) was Sherlock Holmes, which sleuthed $16.6 million in its third weekend for a hearty cumulative gross of $165.2 million. Alvin and the Chipmunks: The Squeakquel captured third place with $16.3 million, bringing its total to $178.2 million. Can you say Threequel? At No. 4 was the new Ethan Hawke vampire thriller Daybreakers with $15 million — an impressive number considering the long-delayed film had a reported budget of just $20 million. The romantic comedy It’s Complicated rounded out the top five with $11 million.

The weekend’s other two new releases — the Amy Adams romantic comedy Leap Year and the Michael Cera teen comedy Youth in Revolt — debuted in sixth and ninth place with $9.2 million and $7 million, respectively. Those are decent numbers, especially considering that both films had budgets of less than $20 million. Still, after the multiplex closes for the night, the Na’vi can’t help but tease poor Michael Cera, a.k.a. “the Sky Person who grossed only $7 million.”