With the summer season officially coming to an end this weekend, overall box office receipts are lagging slightly behind the same period last year.

To date, summer B.O. totals stand at $4.05 billion vs. the record-breaking $4.19 billion earned in 2009. And despite lower average ticket prices ($7.88) during the second quarter, admissions are still down 2.6% from last year, which benefited from an additional week during the summer.

Some B.O. observers expect this weekend’s new entries to each open near the mid-teens, so the battle to surpass last summer’s totals will come down to the wire.

And while Labor Day weekend marks the last gasp of the summer play period, the holiday typically denotes a considerable slowdown at the box office, as moviegoers spend the weekend outdoors. Last year, however, auds shelled out some $125 million over the long weekend, and a number of titles overperformed.

This year’s Labor Day crop includes a mix of titles led by 20th Century Fox’s Robert Rodriguez-directed “Machete” and New Line’s “Going the Distance,” with Warner Bros. distribbing. Focus Features will get the jump on the weekend by opening its George Clooney thriller “The American” today at 2,721 locations before expanding Friday to 2,823.

Despite a few notable disappointments, several blockbusters held on tight to ride the summer box office for several weeks to boffo results.

Disney’s 3D toon “Toy Story 3” leads the summer pack, totaling a standout $405.8 million since its June 18 release. No. 2 grosser is Paramount’s “Iron Man 2,” with a $312.1 million domestic cume.

“Toy 3” ranks as the Mouse House’s second-highest domestic grosser ever, behind 2006’s “Pirates of the Caribbean: Dead Man’s Chest” ($423.3 million), and the toon stands as the only animated film to generate more than $1 billion in worldwide totals.

Meanwhile, “Iron Man 2,” with worldwide B.O. receipts totaling $617 million, surpassed the original franchise offering, which cumed $557.9 million globally.

Topnotch perfs for both “Toy 3” and “Iron Man 2” points to a summer trend of highly successful family-friendly and fanboy pics, as well as popular franchise retreads.

While 3D pics jostled for available screens, Universal’s 3D animated offering “Despicable Me” was tops at the box office, earning $236.6 million domestically. Toon has maintained a steady hold from week to week and likely will outdistance “Shrek Forever After” to become the domestic B.O.’s fifth-highest grosser this summer. “Shrek,” from Paramount and DreamWorks Animation, has cumed $238.1 million.

Animated pics have fared best with the 3D format this summer, though opening 3D shares saw a steady decline because of a crowded slate. “Alice in Wonderland” opened March 5 with 71% of its take from 3D, while “Toy 3” was down 11% from that when it launched June 18.

Yet the frame’s most recent 3D offering “Piranha 3D” bowed with 95% of its opening from 3D-equipped screens, which accounted for 89% of the pic’s opening location count. Some insiders suggest the overwhelming percentage from 3D locations for “Piranha” is due to more 3D-equipped screens available.

In the No. 3 spot this summer, Summit’s latest “Twilight” offering, “Eclipse,” has posted $298.1 million, enough to surpass “New Moon,” which earned $296.6 million domestically last year. Following “Eclipse” in the summer standings, Warner Bros.’ “Inception” became one of the sesh’s biggest surprise hits, given the film’s complex storytelling. “Inception” has tallied $271 million in U.S. receipts; international totals were $387 million as of Sunday.

Warner prexy of domestic distribution Dan Fellman credited moviegoers for embracing an original, nonsequel pic during the summer. “Good movies rise to the occasion, and when you have great movies, you want them to be released in a period of time when most audiences are available,” he said.

It wasn’t as dire a season for nonsequel, nonfranchise fare as some observers opined; “The Other Guys” and “The Expendables” were two that worked better than expected. But others did not develop much support among moviegoers, including Fox’s “Knight and Day” and Universal’s “Scott Pilgrim vs. the World.” “Knight” has cumed a less-than-stellar $76 million; “Scott Pilgrim,” $26.5 million.