AUSTIN — Less than 24 hours after his Texas defense was embarrassed by BYU’s running attack, Manny Diaz was let go.Texas announced Sunday afternoon that the Longhorns defensive coordinator had been fired. Greg Robinson, who served as co-defensive coordinator with secondary coach Duane Akina in 2004, will replace Diaz. “Our performance on defense last night was unacceptable, and we need to change that,” Texas head coach Mack Brown said. “[Robinson] knows this place, did a terrific job in leading our defense before, and I’m excited to have him back on the field.”Missed tackles that plagued the Longhorns last season were a problem again in Texas’ 40-21 loss in Provo, Utah, on Saturday night. The Cougars piled up 550 rushing yards, the most allowed by the Longhorns in school history. BYU quarterback Taysom Hill accounted for 259 of those rushing yards and scored on runs of 68, 20 and 26 yards. “This is a tough deal for everyone involved,” Robinson said. “I know the staff, have a lot of respect for them and am excited for the challenge moving forward. I’ve been around the team a lot, watched all of their film and have been self-scouting and scouting opponents since I came on board in July.”Robinson, 61, rejoined the Texas coaching staff this off-season when he was hired as a football analyst. He went 10-37 in four years as Syracuse’s head coach after his stint with the Longhorns. Robinson, who served as Michigan’s defensive coordinator from 2009-10, has also spent 10 years as an NFL defensive coordinator. “We’re very fortunate that Greg has been around, watched all of our practice video and has a good scouting report moving forward,” Brown said. “His familiarity with the staff and players should make for a smooth transition.”Diaz was reassigned to an unspecified position in the Texas athletic department. In his first year on the job in 2011, Texas allowed 96.2 rushing yards per game, the seventh fewest in the country. Since the beginning of the 2012 season, the Longhorns have given up 210.1 rushing yards per game. Robinson will join the Longhorns’ staff Monday to assist with the team’s preparation for its game against Ole Miss on Saturday. The Longhorns will face Rebels quarterback Bo Wallace, who has completed 63 percent of his passes this year.“I need to get with the staff, work with them to get a plan in place and hit the ground running,” Robinson said. “It’s critical for me to get with [the defensive coaches] and figure out what specifically we need to do moving forward. Having coached here, I do know the ins and outs and having the stability with the rest of the staff will be very beneficial.”Texas went 11-1 in the only season Robinson served as its co-defensive coordinator, ending the 2004 season with a 38-37 win over Michigan in the Rose Bowl. The Longhorns allowed 320.1 total yards per game that year. An average of 107.4 of them came on the ground, compared with the 327 rushing yards per game Texas is surrendering this year, the third most in the nation.Robinson said that he has watched the team even before he was hired this summer on the Longhorn Network. Since his hiring, he has worked mostly from home.Once a distant but experienced and useful resource, Robinson is now a central decision-maker, responsible for turning around a struggling Texas defense.