BERLIN, Aug 12 (Reuters) - Promoted Karlsruhe stunned German Cup winners Nuremberg 2-0 on Sunday while MSV Duisburg, another side back in top flight, upset Borussia Dortmund 3-1 in the Bundesliga. Hungary midfielder Tamas Hajna scored both goals for Karlsruhe, tapping in a rebound off the crossbar a minute before the break and pouncing on a loose ball after Nuremberg goalkeeper Jaromir Blazek mishandled a shot in the 74th minute. Nuremberg, who lost only two home matches last season, finished sixth in the Bundesliga and beat champions VfB Stuttgart in the German Cup final in May. Karlsruhe, back in the top flight after being relegated nine years ago, were the class act of the second division last season and finished first with a league-leading 69 goals. Duisburg, also promoted, won at Dortmund for the first time in 35 years. Nigeria's Manasseh Ishiaku scored twice and Mihai Tararache converted a penalty before Florian Kringe got one back four minutes from time.