By Andrew Downie

RIO DE JANEIRO (Reuters) - Rampant Germany hammered Portugal 4-0 to progress to the semi-finals of the men's football tournament on Saturday, where they will face Nigeria, who beat Denmark 2-0.

Arsenal's Serge Gnabry scored the opener for the Germans with a lovely angled shot seconds before half time and Matthias Ginter added a second with a commanding header from a corner 12 minutes into the second half.

Davie Selke got a third in the 75th minute with a goal that was almost identical to the first, then substitute Philipp Max put the icing on the cake when he ended a sweeping move with a neat finish into the top corner three minutes from time.

The result was payback for Portugal's 5-0 hammering of Germany in the semi-finals of the European under-21 championship last year.

Germany will face Nigeria in Wednesday's semi-final in Sao Paulo after the Africans got a goal in each half to overcome Denmark.

Chelsea's Obi Jon Mikel put Nigeria ahead after 16 minutes when he side-footed home from the edge of the six-yard box after Imoh Ezekiel had set him up.

Aminu Umar doubled their lead with a glancing header, or perhaps shoulder, from a corner with 58 minutes gone.

The other semi-final line up will be decided later on Saturday when South Korea take on Honduras and hosts and three-times runners-up Brazil play Colombia.

The Olympic tournament is restricted to under-23 teams with three overage players allowed per side. Germany have never won it as a unified nation although communist East Germany won gold in 1976.

(Editing by Brian Homewood and Susanna Twidale)