OMAHA, Neb. — Shavon Shields scored 18 points and Terran Petteway had 13 of his 18 in the second half to lead Nebraska to a 68-62 upset of No. 17 Ohio State on Monday night, the Buckeyes’ fourth straight loss.The Cornhuskers (9-8, 1-5 Big Ten), who ended a five-game losing streak, survived after squandering a 14-point first-half lead. They used a 16-5 run late in the second half to regain control and made 13 of their last 16 free throws to hold off the Buckeyes (15-4, 2-4).It was Nebraska’s first win in 16 games against ranked opponents and prompted the student section to pour onto the court after the final buzzer.