Pat O’Brien will be sitting in the co-anchor’s chair next to Giselle Fernandez when “Access Hollywood” begins its second season next month.O’Brien, known for his work with CBS Sports and as a substitute anchor/special correspondent for “Entertainment Tonight,” will replace Larry Mendte on the syndicated entertainment magazine strip starting Sept. 8. Mendte is moving on to a news anchor’s slot with NBC O&O WCAU Philadelphia. Although Mendte’s departure was characterized by all sides as amicable, “Access” insiders say he was considered a weak link on a show already struggling to find a national audience. “Access,” produced by NBC and distributed by Twentieth TV, has averaged a 2.7 national Nielsen household rating in its first year. O’Brien was briefly in the running for the “Access” co-anchor spot early on, but “the timing just wasn’t right for both of us,” said “Access” exec producer Jim Van Messel. “But it was always in the back of my mind that we would work together. He’s a great broadcaster and he’s going to be a great addition to our show.” O’Brien and Van Messel worked together during the latter’s eight-year tenure as exec producer of “Entertainment Tonight,” but they’ve known each other since the early 1970s. O’Brien’s work for CBS Sports has included 1992 and 1994 winter Olympics, NBA, NFL telecasts and the U.S. Open tennis tournament, among other events. He’s hosted the “Beyond Belief” series of primetime specials for CBS and currently co-hosts the “How’d They Do That” series on the Learning Channel. He’s also a featured columnist for the magazines Inside Sports and Live.