MILAN - AC Milan reached the knock-out stage of the UEFA Champions League after they held Ajax to a goalless draw at home on Wednesday.

The hosts were reduced to 10 men with only 22 minutes into play when captain Riccardo Montolivo was sent off for a lunge on Christian Poulsen, but Ajax were unable to secure the victory they needed to progress from Group H.

Poulsen was denied by the post before Montolivo saw red and Serie A outfit Milan dug deep with a dogged defensive display to secure second place behind Barcelona.

Ajax were totally dominant but failed to make the most of their numerical advantage as they missed a golden opportunity to reach the last 16 for the first time in eight years and were forced to settle for a UEFA Europa League spot.

Milan head coach Massimiliano Allegri admitted he "lost weight" with the stress of watching the draw.

"It was a long sigh of relief because this was an important achievement and it wasn't easy to play against Ajax with 10 men," he said.

"The lads were very organized and only ran risks on a few crosses into the box, while Christian Abbiati did well on his saves. Mario Balotelli took the team upon his shoulders, earned free kicks and held the ball up, so he was crucial," he said.

"Ah well, that's the way it went and we all lost a few kilos suffering on the touchline," Allegri added.