Four Down, Four Move On: A Recap of the Champions League Knockout Stage

Well, after a three-week wait, we finally know which four sides will advance into the Champions League quarterfinals and which four are sent packing after only partly successful European campaigns.

The four sides that have advance are English Premier clubs Arsenal and Manchester United, German giant Bayern Munich, and perennial French contenders Lyon.

The four sides that will not see any more Champions League football this year include Portuguese club FC Porto, Italian sides Fiorentina and AC Milan, and Spanish superclub Real Madrid.

Now that these four ties have been decided, here is a look back at each matchup; why each side was able to advance or failed to advance, and what they need to do if they are going to go even deeper than the quarterfinals.

Arsenal v FC Porto

Result of First Leg: Porto 2 Arsenal 1

Result of Second Leg: Arsenal 5 Porto 0

Arsenal advances 6-2 on aggregate

Why Arsenal were able to advance

Despite the fact that they were without captain Cesc Fàbregas due to a hamstring injury, Arsenal played one incredible match at the Emirates as they annihilated FC Porto by a 5-0 score.

The combination of Nicklas Bendtner and Samir Nasri were just spectacular for the Gunners, as Bendtner had a hat trick and Nasri had one incredible performance as Arsenal looked like a side that could make the Champions League final.

For Bendtner, this performance certainly makes up for the misses he had the match prior against Burnley when he missed several golden opportunities, and Arsenal as a whole played perfectly.

Why Porto failed to advance

Porto have not had the best season, and pretty much every player had a match to forget as Porto had no answer to the Arsenal attack.

The only solid player for Porto was Helton, who allowed five goals. However, his defense was clearly the reason why he did so terrible, and the Brazilian keeper will now have to focus on getting into the Champions League for next season.

But that is an extremely difficult challenge for Porto, as they currently find themselves behind league leader Benefica by 11 points in March.

What Arsenal must do in order to advance from the quarterfinals

As long as Arsenal put a performance like this together every time they play, they will be unstoppable and could make the Champions League final.

But they will need to have complete focus from everyone and will need to make sure they have no more games such as the first leg in Porto again.

Fiorentina v Bayern Munich

Result of First Leg: Bayern Munich 2 Fiorentina 1

Result of Second Leg: Fiorentina 3 Bayern Munich 2

Score tied at four all on aggregate (Bayern Munich advance with two away goals).

Why Bayern Munich were able to advance

Even though they were extremely lucky in the first leg with help of referee Tom Øverbø, Bayern proved to us that they are a side that is capable of a deep run in Europe by advancing on away goals against Fiorentina.

Great goals from Mark Van Bommel and Arjen Robben did prove to be enough for Bayern to advance on away goals, even though Bayern lost the match.

Why Fiorentina failed to advance

Even though the Viola played a great match, the terrible officiating from the first leg proved to poison Fiorentina in the second leg as they failed to advance.

Now, the Viola's chances of playing in any European competition next year are very slim due to the fact that they are 10th in Serie A.

What Bayern Munich must do in order to advance from the quarterfinals

Bayern will need to play much better than they did against Fiorentina if they are to advance past the quarterfinals.

The Bayern defense was just terrible against Fiorentina, and they should hope that they don't have to face a Barcelona or Arsenal in the quarterfinals.

Manchester United v AC Milan

Result of First Leg: AC Milan 2 Manchester United 3

Result of Second Leg: Manchester United 4 AC Milan 0

Manchester United advance 7-2 on aggregate

Why Manchester United were able to advance

In what was the most hyped of all of the Champions League ties, Manchester United showed us why they are one of the best sides in the world after dumping AC Milan out of the Champions League.

This mainly happened due to the 4-0 demolition at Old Trafford in the Second Leg, as Wayne Rooney and his four goals during this draw has showed us that he could lead Manchester United to victory against even the best.

And of course, with the Old Trafford advantage, it will be extremely difficult to dump Manchester United out of the Champions League this season.

Why AC Milan failed to advance

With the return of David Beckham to Old Trafford and after not suffering away from the San Siro in the Champions League, AC Milan were dumped out by a pressing Manchester United side that were more hungry to win.

Milan did have several good opportunities to score, but they weren't able to beat Edwin Van der Sar as the Rossoneri will have to go another season without winning the Champions League.

What Manchester United must do if they are to advance past the quarterfinals

As long as Manchester United continue to have performances such as these, they will be extremely hard to beat.

Wayne Rooney has proved that he is capable of leading Manchester United to the Champions League final, and as long as he is healthy, we might see Manchester United at the Champions League final on May 22.

Real Madrid v Lyon

Result of First Leg: Lyon 1 Real Madrid 0

Result of Second Leg: Real Madrid 1 Lyon 1

Lyon advance 2-1 on aggregate

Why Lyon were able to advance

In what has been the biggest surprise of the Champions League knockout stage to date, Lyon have taken out the Real Madrid squad consisting of stars such as Cristiano Ronaldo and Kaka as they were able to get a crucial away goal by Miralem Pjanic in the 75th minute.

Lyon did concede an early goal to Cristiano Ronaldo, but they successfully stopped the Real Madrid attack for the rest of the match as they will go onto the Champions League quarterfinal for the first time since 2006.

Why Real Madrid failed to advance

Despite dishing out over 200 million pounds on new players last summer, Real Madrid now have seen their dreams of a 10th Champions League title (which will be played at their home stadium, the Bernabeu in May) as they could get a crucial goal against Lyon.

The main reason why Real Madrid failed to advance was that they were incapable of getting any more goals after Ronaldo scored in the sixth minute, and now they will have to wait until next year to win again.

What Lyon must do to get past the quarterfinals

Lyon have really showed us with their strong defense and timely goals, they are capable of beating anybody.

They can play against anyone, and with wins against Liverpool, Fiorentina, and now Real Madrid in the Champions League this season, they might finally be able to get to the Champions League final.

Finally, we have seen four great matchups sadly come to an end as Porto, Fiorentina, AC Milan, and Real Madrid are out of the Champions League while Arsenal, Bayern Munich, Manchester United and Lyon have now all advanced.

Now with the other great matchups in the Round of 16 next week, this could really shape up to be an even greater Champions League season as even the European football giants could fall.