I was talking to some family members tonight, thinking of when our last Top 20 true road (not neutral site) night game win was. We were torturing ourselves with how we've recently come up short in these games--Wisconsin, Ohio State, Michigan State come to mind.
If you count neutral site games I believe it is 1997 Big XII champ over A&M.
If you count only true road games...anyone know??? Wikipedia doesn't list time of game pre-1989