Anderlecht enjoyed by far the better of the chances in a goalless first half. Ulreich, deputising for the injured Manuel Neuer in the Bayern goal, produced a series of clutch saves from Poland striker Lukasz Teodorczyk (twice) and Dennis Appiah to keep his side on level terms going into the break.

Second-half goals from Robert Lewandowski and Corentin Tolisso made the Belgian champions pay for their profligacy in front of goal -- and kept their hopes of topping the group alive, after Sofiane Hanni's equaliser had restored parity for the Belgian champions just after the hour mark.

However, Heynckes was far from content with his side's display, despite securing his ninth consecutive Champions League win.

"I had to give a few clear instructions at the half-time break, because we played especially badly in the first half," he said. "We allowed three or four clear goalscoring chances that Sven Ulreich brilliantly kept out.

"I didn't recognise the team in the first half, so I had to explicitly discuss these things. We played carelessly and gave the ball away far too easily.

"Anderlecht had not won a single point, we thought it would be an easy game -- but you cannot afford to think like that these days.

"I want to pay a compliment to our opponent, they played excellently."

Heynckes' mood was further darkened by the loss of Robben and Thiago to injury. The Spain international had to be replaced by James Rodriguez on the stroke of half-time.

Heynckes said: "I cannot give an exact diagnosis immediately after the game, but Thiago was in no pain beforehand but he did have this injury leftover from the international break with bruising -- so it could be connected to that."

However, the 72-year-old added: "I think Thiago has a serious muscle injury."

Thiago was seen leaving the stadium on crutches and sporting director Hasan Salihamidzic told reporters he expects the Spain international "to be missing for several months."

Meanwhile, the news was more encouraging for captain Robben, who went off clutching his thigh three minutes after half-time.

"With Robben we have to see. He believes it's not too bad but we cannot afford anymore injuries -- our cover is becoming thinner and thinner," Heynckes said.

Meanwhile, goalkeeper Ulreich told Sky Germany: "I'm happy to have pulled out a few saves, especially in the first half to stop them scoring. Of course, that was not how we had intended to play.

"We lacked concentration, gave the ball away far too easily and allowed Anderlecht space to play, so obviously we are not completely satisfied."

After a 3-0 defeat against Paris Saint-Germain which prompted the sacking of Carlo Ancelotti, Bayern can still top the group with a 4-0 win over PSG in their final group game.

"We will need a different performance against PSG," Ulreich said.

"We will have to step things up and be a lot more focused. We have to make amends against them."

Defender Jerome Boateng also bemoaned Bayern's below-par display, but also hailed his goalkeeper's performance.

"It was a fortunate win. Anderlecht was more aggressive and we were sleeping for the whole of the first half. We cannot be pleased -- this is our standard," Boateng told ZDF. "We have to thank Sven Ulreich."