There was late drama in the Champions League on Wednesday night as Tottenham Hotspur pulled off the unthinkable to reach the final at Ajax's expense.
Trailing 1-0 from the first-leg at the new Tottenham stadium, the Lilywhites travelled to Amsterdam knowing they had to score at least twice in order to retain hope of setting up a meeting with Liverpool next month.
Amazingly Spurs were on the brink of elimination heading into the final minute of injury time, but Lucas Moura completed his hat-trick to ensure the north London outfit prevailed by virtue of the away goals rule.
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The good news for Arsenal and Chelsea - who face Valencia and Frankfurt respectively - in the Europa League semi-finals tonight is that away goals do count for the remainder of the competition this season.
Arsenal travel to the Mestalla with a 3-1 advantage, but as the last two days have shown, anything can happen when it comes to European football - especially in the knockout stages.
Here's how the away goal rule could come into play if Arsenal score tonight.
Live match updates from Valencia v Arsenal HERE
The rule, which comes into effect in the result of a draw on aggregate after the second leg, first emerged in 1965 and was established in UEFA competitions towards the end of the decade - and has stood ever since.
Should the Gunners score once, Valencia will need to score four times to progress, making it 5-4 on aggregate.
Arsenal would have the away goal advantage in this scenario, meaning Los Che will be knocked out if the two teams are drawing at the final whistle.
Although, Valencia would go through on the away goals rule should they win 2-0 thanks to Mouctar Diakhaby's strike at the Emirates.
The only way we'd get extra time and possibly penalties is if Valencia win 3-1.
The away goal rule does count in both periods of extra time. If Arsenal score in extra time, Valencia must score twice in order to progress.
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Live match updates from Chelsea v Frankfurt HERE
Here's how the away goal rule could come into play if Frankfurt score tonight.
Should Frankfurt a score once, Chelsea will need to score twice to progress, making it 3-2 on aggregate.
The only way we'd get extra time and possibly penalties is if it finishes 1-1.
Fans of the away goal rule should cherish it, as it may not be around for too much longer.
This is because there's talk of UEFA changing the rule ahead of the 2019/20 season.
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