Paramount's Iron Man and Fox's What Happens in Vegas held up well in their third and second weekends respectively, but Warner's Speed Racer lost more power after its disappointing start last week.
Prince Caspian, produced by Walt Disney Studios and Walden Media, opened in 3,929 cinemas and easily topped the box office chart, averaging $14,398 per theatre.
However the family fantasy sequel had been expected to beat the $65.6m opening achieved in December 2005 by The Lion, the Witch and the Wardrobe, the first film based on C S Lewis' Narnia children's books. Some forecasts even suggested that with no new wide-release competition and a PG rating Caspian, which got mostly positive reviews, would open with more than $80m for the weekend.
In the event, the big budget epic - directed once again by Andrew Adamson, with British up-and-comer Ben Barnes joining the cast in the title role - may have suffered from a long running time, stronger than expected holdover competition and the fact that school holidays have not yet started.
With the new Indiana Jones film opening on Thursday, Caspian may now struggle to equal the $291.7m domestic take of The Lion, the Witch and the Wardrobe, which displayed strong legs over its winter holiday season run.
After two weeks on top, Paramount's Iron Man fell 39% to $32.2m from 4,154 cinemas (for an average of $7,510). That pushed the comic book blockbuster's domestic total to $222.5m.
Fox's romantic comedy What Happens in Vegas, which pipped Speed Racer for second place last week, slid 31% in its second weekend to $13.8m from 3,255 theatres (average - $4,254), for a total of $40.3m.
In its second weekend, Warner's under-performing Speed Racer was down 59% to $7.6m from 3,606 theatres (average - $2,120), for a $24.4m total.
Other rom-coms also showed staying power this weekend: Universal's Baby Mamma was down only 26.2% in its fourth week to $4.6m, for a total of $47.3m; Sony's Made of Honor dropped 44.6% in its third week to $4.5m, for a $33.7m total; and Universal's Forgetting Sarah Marshall was off 33.9% in its fifth week to $2.5m, for a $55m total.
Overture's The Visitor sneaked into the top ten, dropping only 6% in its sixth week to gross $687,000, for a $3.4m total.
Overall, it was a down weekend as the height of the summer season approaches. In total, the weekend's top ten films made 27% less than the top ten from the corresponding weekend last year.
The only wide release next weekend - the Memorial Day holiday weekend -- is Paramount's long-awaited sequel Indiana Jones and the Kingdom of the Crystal Skull, with Harrison Ford returning in the title role for director Steven Spielberg and Shia LaBeouf also starring.
Estimated Top 10 North America May 16-18, 2008
Film (Dist)/Int'l dist/Est wkd gross/Est total to date
1 (-) The Chronicles of Narnia: Prince Caspian
(Buena Vista) WDSMPI $56.6m -
2 (1) Iron Man (Paramount) PPI/Various $31.2m $222.5m
3 (2) What Happens In Vegas (Fox) Fox Int'l $13.8m $40.3m
4 (3) Speed Racer (Warner Bros) WBPI $7.6m $23.4m
5 (5) Baby Mama (Universal) UPI $4.6m $47.3m
6 (4) Made Of Honor (Sony) SPRI $4.5m $33.7m
7 (6) Forgetting Sarah Marshall (Universal) UPI $2.5m $55.1m
8 (7) Harold And Kumar Escape From Guantanamo Bay
(New Line/Warner Bros) NLI $1.8m $33.9m
9 (8) The Forbidden Kingdom (Lionsgate/TWC)
TWC/Mandate Int'l/Relativity $1m $50.3m
10 (13) The Visitor (Overture) K5 Intl $687,000m $3.4m