Fiona and Shrek in 'Shrek Forever After'In another slow week at the summer box office, it was once again the ogre who was the biggest source of green. 'Shrek Forever After' fought off challenges from a rock star, an assassin, a Great Dane and a mutant to top the chart for the third straight week.

As expected, 'Shrek' dipped about 40 percent from last week to finish with an estimated $25.3 million. It's still underperforming compared to the first three 'Shrek' movies, but this weekend's haul brought it that much closer to the $200 million mark, a threshold that only 'Iron Man 2,' among all this summer's movies so far, has crossed.

Among new releases, 'Get Him to the Greek' fared best. The comedy debuted at No. 2 with $17.4 million. Its per-screen average of $6,460 was the best of all current wide-release movies. Action/romance 'Killers' was close behind, opening at $16.1 million for a third-place finish.