Real Madrid vs Atalanta was finely-poised coming into their Champions League second leg.

As much as Los Blancos entered their round of 16 tie as heavy favourites, you only have to look at Atalanta's incredible European run last season to appreciate the threat they pose.

And you really have to wonder whether the plucky Italians would have pulled more than a 1-0 deficit into the second leg in Madrid if it wasn't for Remo Freuler's 17th-minute red card.

Real Madrid vs Atalanta

In the end, Ferland Mendy's late strike was enough to secure the victory for Zinedine Zidane's men, but they could be sure that the Bergamo club were going to give them hell in the return tie.

However, the Champions League's most successful team were sure to assert their authority early on, taking the lead after 35 minutes as Karim Benzema bagged yet another crucial goal.

But Atalanta weren't simply going to curl up and die, instead knocking on the door for an equaliser and coming within a few inches of creating a clear opportunity just before the half-time whistle.

Controversial half-time whistle

And we mean that literally because the phrase 'just before the half-time whistle' was exactly what made Atalanta's massive opportunity in the Spanish capital so controversial.

There was uproar on social media when images emerged of the clock hitting 45 minutes when Atalanta looked to be clear through on goal with the referee having called time too early.

As a result, the Champions League official came under fire for what JOE branded as 'probably the worst half-time whistle of all time' - and you can check out some of the reaction below:

What on earth has gone wrong there!?

According to Football Italia, the Atalanta bench and staff, as well as the Sky Sports Italia commentators, 'vented their irritation' with Danny Makkelie's early whistle - and it's easy to see why.

Difficult situation to judge

Now, it is worth saying that the whistle had been blown by the time the ball reached Luis Muriel, but that will do little to temper Atalanta's anger because that was still before 45 minutes on the dot.

Besides, as the images show, the ball was about to play Muriel clean through on goal by the time the first-half was officially completed. 

So, sure, there's good reason to think that Raphael Varane would have cut out the ball, but it's the fact that Atalanta never got to find out when they should have done that is so disappointing.

After all, if Varane's performance against Manchester City last season taught us anything, it's that you can never be certain in the beautiful game and Atalanta could well have benefitted.