Bayern Munich coach Pep Guardiola and German international star Thomas Mueller have bemoaned the trend of Bundesliga teams using a five-man defence to try to hamper the Bavarian giants' run to the league title.

Javi Martinez scored his first Bayern goal for two years on Saturday in Munich's 3-1 win at Schalke 04 which opened an eight-point lead in the German league.

Bayern are bidding to become the first team to win a fourth straight Bundesliga crown and have won 12 of their 13 games so far this season with just a goalless draw at Eintracht Frankfurt to blot their perfect record.

David Alaba's early goal at Gelsenkirchen's Veltins Arena was cancelled out by Schalke's Max Meyer before Martinez, then Mueller struck for Bayern.

Schalke played a back three with two wing backs and Mueller said it is becoming common practice for teams to focus on defence when they come up against Bayern's goal-scoring machine, which has netted 40 goals in 13 league games this season.

"You have to work for every victory in the Bundesliga and we always have to go to 100 percent," said Mueller.

"Opponents don't make it easy and recently the five-man defence has become fashionable.

"I don't know if supporters like it so much, but the opponents try and stop everything."

Guardiola also criticised the Veltins Arena pitch as well as Schalke's defensive tactics.

"It was hard to win here," said the Spaniard. "The pitch here wasn't good and it's not easy to attack a five-man defence with a four-man midfield."

Bayern took a fortuitous lead in Gelsenkirchen when Alaba's long-range shot clipped Leon Goretzka's heel and flew into the Schalke net with nine minutes gone.

Schalke drew level through Meyer's superb goal on 17 minutes when he turned Bayern captain Philipp Lahm and powered his shot past goalkeeper Manuel Neuer.

But Bayern maintained their unbeaten record in Germany's top flight when Spain's Martinez headed Arjen Robben's pin-point cross on 69 minutes.

It was the centre-back's first league goal for Bayern since August 2013, then Mueller added a late third by curling his shot inside the far post.

There was a minute's silence at all Bundesliga grounds -- the players also wore black armbands -- out of respect for the victims of the Paris terror attacks.

And Mueller said it was important to get back to playing for several reasons.

"It was imporant that we could play football again," said the Germany international.

"It was important for the spectators, for us players and for the whole league."