In the FIFA World Cup knockout rounds, sometimes a simple errant mistake in defense can mean heartbreak for a whole nation. And with Switzerland and Argentina meeting in the round of 16 tie on Tuesday in Sao Paulo, the real questions originate in both teams defenses. Argentina come into the match having won their group, albeit unconvincingly, on the heels of "Messi Magic" -- The Flea has scored four goals in their three matches, including a stoppage-time game winner against Iran. Otmar Hitzfeld's Switzerland qualified to the knockout stages despite a 5-2 hammering from France, which showed their defensive frailties. In this inter-continental clash, one moment of wizardry -- or lapse of concentration -- can settle the score and decide who continues in this tournament of surprises. 

Argentina come into the match on the heels of three consecutive victories: 2-1 against Bosnia-Herzegovina, 1-0 against Iran, and 3-2 against Nigeria. The common themes throughout their performances have been an over-reliance on Lionel Messi, and a less-than-convincing back line and goalkeeper. Alejandro Sabella will need Javier Mascherano to be at his best to stop the quick counters sparked by Xherdan Shaqiri, who scored a hat trick in Switzerland's final group stage game against Iran. But it is up-front where Argentina face unexpected problems. Sergio Aguero, the Manchester City striker, is out for the rest of the tournament having sustained a muscle tear injury in Argentina's final group stage game against Nigera, and it looks like Paris St. Germain man Ezequiel Lavezzi will be his replacement. Alongside Messi and Gonzalo Higuain, this is still no attack to scoff at, and with the delivery quality of Angel di Maria, the Argentine attack is perhaps still the most lethal left in the tournament. 

Switzerland, who are dubiously ranked sixth in the world, have so far under performed in this years edition of the Cup. A last ditch winner was needed to see off a stubborn Ecuador side, but it was in their second game against France, where the true problems emerged. Lackluster defending, coupled by slow build-up, made it easy for the French to demolish the Swiss, who were down five goals before even grabbing their first. Their victory over Honduras in their final game was expected, but a brilliant performance by Shaqiri showed the young talents great ability. However, against an Argentinean side with this much attacking prowess, their true test will come in defense, where they will need to be organized and focused if they wish to see anything out of this match.

All in all this should be an exciting encounter from both teams who have to make a point. Argentina will look to get a quick start, much like they did against Nigeria, while Switzerland will have to do whatever is necessary to stop the powerful Argentine strike force. Expect Messi to penetrate the Swiss defense on numerous occasions from fairly deep, as he's been doing, and perhaps even add to his goal-tally. This is Argentina's game to lose, but in this World Cup, anything is possible. 

The game is set to kick off at 12:00PM EST at the Arena de Sao Paolo in Sao Paolo. It can be seen on ESPN and in Spanish on Univision. If you want to live stream the match, simply go to WatchESPN here and here for a live stream in Spanish.