Mike Penders has just exposed Chelsea's biggest problem, and it's very worrying

Mike Penders has admitted Chelsea struggled to cope with Sunderland's physical approach during their defeat at the Stadium of Light, and it's a problem Xabi Alonso needs to solve.

The Blues arrived expecting a difficult afternoon, but they were unable to find a consistent way through Regis Le Bris' side. Sunderland made life uncomfortable from the first whistle, competing aggressively and refusing to give Chelsea the space they wanted.

Penders' post-match comments are concerning too. The goalkeeper acknowledged that Chelsea struggled to find a way to break the Black Cats down once they dropped deeper and put almost every player behind the ball.

Speaking after the defeat, Penders admitted Chelsea were disappointed with the result but recognised how difficult it was always going to be playing at the Stadium of Light.

"Very disappointed with the result. You know when you come here to their stadium that it will be a difficult game, and they fought very hard," he told the official Chelsea website.

The goalkeeper went on to explain how Sunderland's aggressive approach made it difficult for Chelsea to settle into the game.

"At one point, it went very fast from side to side. Sometimes we had control and, of course, in certain moments when you go higher up the pitch they will be very aggressive and the way they play is very difficult," he added.

That was a major part of the problem for Alonso's side. Sunderland were prepared to compete physically, press aggressively and disrupt the away side whenever they tried to build attacks.

He continued: "In the second half they dropped very low and had every man behind the ball, so we had a bit more control and we had to push. We had some chances, but it was difficult against 11 behind the ball to find the right spaces. We kept pushing, especially in the last 15 minutes, we kept dropping balls at them, but it wasn’t enough."

Chelsea created some opportunities but could not find a way through. Penders admitted that even their late pressure, which involved repeatedly delivering balls into the Sunderland penalty area, was not enough.

There is a worrying pattern emerging when Chelsea come up against teams prepared to make games physical.

Sunderland were not interested in allowing the Blues to play their usual passing game without a fight. They pressed when the opportunity presented itself, competed for second balls and made sure Chelsea had very little time to make decisions.

When they eventually dropped deeper, they were just as difficult to break down. Chelsea had more possession and control in the second half, but they still struggled to turn that dominance into clear-cut opportunities.

It is not enough for Alonso's side to control possession if they can't find a way to break down opponents who defend with discipline and aggression.

There will be plenty of teams in the Premier League willing to use a similar approach against Chelsea. They know the Blues have technically gifted players, but they can also make life difficult by taking away their time and space.

Alonso needs to find a solution, whether that means improving Chelsea's movement in the final third, being more direct when necessary or simply matching opponents physically.

Sunderland's victory on the weekend provided a blueprint of how to frustrate Alonso's side. The most worrying part is that the Blues didn't have an answer though.