(Reuters) - The "luck of champions" helped Lionel Messi's Argentina scrape into the World Cup last eight on Tuesday past an increasingly daring Switzerland in their quest for a third World Cup.

None of the surviving pre-tournament favorites have had an easy passage into the quarter-finals, with hosts Brazil, Germany and the Netherlands also suffering their share of scares before finally overcoming tenacious opponents.

Angel Di Maria's strike for Argentina two minutes from the end of extra time in their last-16 clash secured a 1-0 victory, although the Swiss almost equalized in the dying moments when substitute Blerim Dzemaili's header struck the post.

"Yesterday Germany, Holland the day before. Nothing's easy, it's all hard work. Football has evolved today and everything's very level," Argentina midfielder Javier Mascherano said.

"We had luck on our side," Man of the Match Messi added.

Argentina's goal came from the only moment in which Messi, well marked by a clockwork-like defense, found the space to make a telling contribution with his pass to Di Maria and the Swiss were for once caught at least a man short in defense.

It was the one telling moment in a disappointing performance by Di Maria, with Argentina still waiting for him and Gonzalo Higuain to find their best form, while Messi clearly missed having the injured Sergio Aguero alongside him.

TACTICAL NOUS

A tournament that began with an exciting group phase full of goals and shock results, has reverted to tight matches, with two going to penalties and another three decided by a single goal before the final match of the first knockout round.

The Swiss, like the other surprise teams in Brazil, gave Argentina a hard time, blocking their path to goal with Messi, unable to score after netting four goals in the three group matches, becoming increasingly frustrated.

More than that they played a big part in a match that could have gone either way, their breaks down the flanks troubling the Argentine defense. Like Chile and Mexico before them, the Swiss would not have been out of place in the last eight.

They showed a tactical organization similar to that displayed by Costa Rica who enjoyed a surprise run through their group with upset wins over Uruguay and Italy, or Algeria in breaking into the last 16 from Group H.

Switzerland, with three members of the 2009 under-17 World Cup winners in their side, owed their second place in Group E to the awareness and concentration they showed in stealing an opening 2-1 win over Ecuador from an added time counter-attack.

Messi's equivalent in the Brazil team, Neymar, has also cut a frustrated figure at times for the hosts whose tortuous path to the last eight also owed a lot to luck as they held out against Chile at the Maracana before winning on penalties.

Organized underdogs look sure to continue to frustrate their more highly-vaunted opponents as the tournament moves towards the final on July 13. Who will win? Lady Luck could decide.