BREMEN - Hamburg SV stunned hosts Werder Bremen 1-0 in their UEFA Cup semi-final first leg on Thursday with Piotr Trochowski's first-half goal putting the visitors in control of the tie. Midfielder Trochowski beat keeper Tim Wiese when he peeled back to the far post to meet a Guy Demel cross and headed it over the helpless keeper in the 28th minute. "We did it well in the first half," Hamburg coach Martin Jol told Premiere television. "But even though they were better in the second we kept creating some chances and overall it is a good result. "We wanted to score a goal and if possible not let one in. Bremen are a very dangerous team and they know how to score goals." Hamburg, beaten by Werder on penalties in the German Cup semi-final last week, were eager for revenge in the northern derby. The visitors were more aggressive in the first half, missing their first chance through Ivica Olic in the second minute when Wiese did well to block his close range effort with his feet. Wiese, who had saved three penalties in Werder's Cup win over their Bundesliga rivals, was challenged again in the 22nd when he palmed away a low drive from Paolo Guerrero, who will miss the return leg following a yellow card. Hamburg will now be hoping injured striker Mladen Petric will be fit by next week to replace the Peruvian. DIEGO STIFLED Trochowski though quickly made amends for the misses six minutes later when he grabbed the only goal with a header. With playmaker Diego largely stifled by a well-organised Hamburg defence, Werder started to probe the flanks in the second half and had several good chances through Hugo Almeida and Claudio Pizarro but neither could convert from close range. Substitute Markus Rosenberg should also have done better in the 71st minute when Mesut Ozil picked him out with a nice pass in the box but he managed to fire over the bar. Pizarro almost snatched a stoppage-time equaliser but again keeper Frank Rost did well to block his shot from six metres, leaving the hosts to rue their missed chances. "We must understand that the game consists of two halves and we sort of missed the start of the game," Bremen coach Thomas Schaaf said. "Then we did improve a lot, we played our game but did not convert any of the several good chances we created."