UEFA Champions League QF: Do-or-die for Madrid, Bayern, Dortmund, Villa in second leg

Several of Europe's top guns face must-win matches as the quarterfinals of the continent's premier football competition enters the second leg

- AGENCIES

Barcelona, Paris Saint-Germain, and Arsenal hold such commanding leads in their Champions League quarter-final matches that a place in the last four looks all but certain.

Don't be so sure. European club soccer's most prestigious competition has a habit of upsetting the odds.

Barcelona and PSG have very recent memories of how quickly things can change. Barcelona were 4-2 up on aggregate against PSG early in the second leg of last year's quarterfinals - only to lose 4-6.

In 2017, PSG led 4-0 after the first leg of a round of 16 game between the two in Paris, but famously lost 1-6 at Camp Nou.

Part of what makes the Champions League such compelling viewing is the fragility of even the most commanding leads.

Liverpool trailed AC Milan 0-3 at halftime of the final of 2005 before staging a dramatic fightback and going on to win in a penalty shootout.

The Merseyside club stunned Barcelona on its way to the title in 2019 when overturning a 3-0 loss in the first leg of the semifinals by winning the return leg 4-0.

There are many more examples of how the tables can be turned when Europe's elite go head-to-head, which is why nothing can be taken for granted ahead of this week's second leg matches.

Record 15-time winner and defending champion Real Madrid will have to produce another of their famous comebacks to overturn a 0-3 first-leg loss to Arsenal.

If anyone can, Madrid can - but it goes into Wednesday's game at the Bernabeu after a run of unconvincing results. Carlo Ancelotti's team has only won one of its last four games in all competitions - Sunday's 1-0 victory against Alaves.

The defeat to Arsenal could have been even heavier after being dominated at the Emirates Stadium and came after Madrid needed a penalty shootout to overcome Atletico Madrid in the round of 16.

But Madrid's history is built on producing special performances in Europe.