Jupp Heynckes was critical of Bayern Munich's second-half display in their 2-0 win over relegation-threatened Mainz on Saturday.

With nearest rivals Schalke losing to lowly Werder Bremen, the Bundesliga leaders extended their lead at the summit to 18 points thanks to first-half goals from Franck Ribery and James Rodriguez.

However, Heynckes was far from impressed with what he witnessed after the break at the Opel Arena, the visitors wasting a number of clear opportunities to increase the final margin of victory.

The experienced coach was far more positive in his assessment of the home team though, praising Mainz - who dropped to 16th due to Werder's surprise win - for their efforts in defeat.

"My team played really well before the break and got off to a good start [in the second half], but we failed to take our chances and extend our lead," Heynckes told the club's website.

"You have to admit that Mainz also had good chances in the second half. You have to take into account that teams surpass themselves when they're in the relegation battle. You've seen it in the case of Werder and also today regarding Mainz.

"We had five or six gilt-edged chances after the break. If we had taken them we could have easily run down the clock. Instead, our opponents had hope and chances again and again.

"We were too sloppy and not as strong as in the first half when it came to transitions from attack to defence.

"Taken altogether the victory was deserved but compliments to Mainz for their display."