Manchester United scripted an amazing comeback to beat Benfica 3-1 in a pulsating contest to finally qualify for the knockout stage of Champions League.

Going by the listless performance for the first half hour United looked to have been playing for a draw, which would have seen them qualify from the group. However a shock Nelson goal in the 27th minute woke up United from its slumber to put up an amazing performance in the second half to win the match 3-1.

Sir Alex fielded his strongest line up at the start. However tactically United started the match in the first gear, with a conservative 4-5-1 formation and passing without any sense of urgency. Till United conceded the goal, they had only one shot on target to show for, and that too came from Rio Ferdinand following a Giggs corner.

With United not showing any urgency of attacking them, Benfica slowly took control of the game. Portuguese winger, Simao ran down the right side to make a pinpoint cross to Nelson, who then hit a first time shot to curl the ball away from van der Sar into the net.

As if realizing for the first time that a loss would mean not qualifying from the group stage for the second time, United started their assault on the Benfica goal. Cristiano Ronaldo's drilled free kick was parried out by keeper Quim, while Saha saw his header cleared off the line.

Rooney joined Saha up front and United continued a relentless attack on Benfica goal. Both Ferdinand and Scholes hit the target but were unable to draw level. United finally scored when Vidic converted a free kick by Giggs one minute into extra time.

United continued the second half in the same vein with Saha and Rooney missing the target. United took the lead in the 61st minute when Giggs headed home a Ronaldo cross to score in the Champions League for the 12th consecutive season.

Though Simao tried to lift his team, making couple of mazy runs, his efforts went in vain as United hammered the final nail in the coffin when Saha scored from a corner taken by Rooney.

Sir Alex looked immensely relieved after the match saying that United can ill afford to make the same mistakes in the knockout round. "I thought the game was too slow to begin with. We are not at our best when we play with patience. We got a break just before half time. The goal woke everyone up, the supporters and the players. We controlled the game in the second half and it was a very good performance after going behind. The team is confident about its ability to play but we can't afford to spurn chances in the next round", he said.

Meanwhile Arsenal secured their berth in the next round following a 0-0 draw at Porto while Milan were beaten by Lille 2-0. The draw for the knockout stage will be made on December 15.

Matchday 6 results:

Dynamo Kyiv 2-2 Real Madrid

Lyon 1-1 Steaua

København 3-1 Celtic

Man Utd 3-1 Benfica

Hamburg 3-2 CSKA Moskva

Porto 0-0 Arsenal

Anderlecht 2-2 AEK