Roughly 7.4 million viewers welcomed Seth, Summer, Ryan and Marissa back from summer vacation last night on The O.C.'s third-season premiere. Although the sudser was off by 13 percent compared to last year's debut, it still ranked a strong No. 2 in its time slot among adults 18 to 49. It also funneled a decent 6.6 million viewers into Fox's new mystery-soap hybrid Reunion.