1. Ronaldo penalty hero as Madrid squeak through

Cristiano Ronaldo was the late hero and English referee Michael Oliver the villain (for some) as Real Madrid just about survived the scare of their lives in the second leg of their Champions League quarterfinal.

Juventus came oh so close to pulling off the biggest shock in European football history -- it would have been even bigger than Roma's comeback against Barcelona last night -- and it all came down to a disputed penalty in the third of three minutes of added time.

Oliver saw a push by Medhi Benatia on Lucas Vazquez. Juve captain Gianluigi Buffon was shown a straight red card for demonstratively sharing his disagreement. It took an age for all the arguments to calm down, and substitute goalkeeper Wojciech Szczesny put on his gloves.

But Ronaldo was the coolest man in a boiling Bernabeu, and he hammered the spot kick into the top corner -- keeping his run of scoring in all 10 Champions League games this season going -- and sending the holders through to the last four.

Madrid's 3-0 advantage from last week's first leg in Turin led to a relatively muted atmosphere pre-game, but Mario Mandzukic's opening goal on 76 seconds changed that completely. The home defence was caught napping by Sami Khedira's run and cross, and the Croatia international had a simple header at the back post. Juve kept coming -- with Keylor Navas saving from Gonzalo Higuain as the Bernabeu gasped for breath.

Madrid then went on the attack themselves -- with surprise starter Gareth Bale denied by Buffon, and Isco having a goal debatably ruled out for offside after the veteran goalkeeper saved from Ronaldo.

It was helter-skelter stuff, with both teams shaking at the back. And the home crowd were really worried when Mandzukic made it 2-0 eight minutes before half-time, with another back-post header, this time from a Stephan Lichtsteiner cross.

Zinedine Zidane made a double switch at the break, removing Bale and Casemiro for Lucas Vazquez and Marco Asensio, and changing to a 4-4-1-1 shape. Madrid had most of the ball, but were not making clear chances. Then on the hour mark, Keylor spilled a simple cross and Blaise Matuidi smuggled the loose ball over the line to level the tie 3-3.

The tension kept cranking higher and higher, as both teams knew one mistake could prove fatal. Buffon later saved Isco's 20-yard skidder, and Ronaldo headed over from eight yards. The Portuguese's moment seemed to have passed -- but there was still time for one last twist in the tale.

2. Buffon final UCL game ends with red

Asked at yesterday's pre-game news conference if this was to be his final Champions League game, Buffon suggested that against Madrid at the Bernabeu was not a bad way to go out. And it was certainly memorable, as the 40-year-old defied time with a series of excellent stops, only to lose his head amid all the penalty drama at the end.

On his 116th Champions League appearance -- 13th on all-time list -- Buffon was an inspirational presence for his team. He made excellent saves from Bale, Ronaldo and Isco through his 92 minutes on the pitch -- and was also constantly organising and motivating his defence, including another fist bump with fellow old warrior Giorgio Chiellini when it seemed the shock comeback was really on.

But things were to turn out differently. Oliver's penalty decision was a tough call to take, although at first glance in the stadium it looked correct. Buffon clearly thought otherwise, and took his remonstrations against the English official too far.

It was all quite reminiscent of Madrid coach Zidane's moment of madness in his final game as a player -- the 2006 World Cup final -- when Italy's Buffon was an interested observer as the France legend threw his head. Gigi's end was not quite as dramatic as Zizou's, but it will not be soon forgotten.

Gianluigi Buffon's Champions League career ended with a red card. VI Images via Getty Images

3. Madrid must resolve issues at back

While most of the pre-game attention focused on Bale ousting Karim Benzema from Zidane's preferred XI, the selection of Jesus Vallejo in place of suspended club captain Sergio Ramos at the back was quickly much more important.

In last weekend's La Liga derbi Atletico Madrid focused their attacks down Madrid's left-hand side, and left-back Marcelo and left-sided centre-back Vallejo were caught out repeatedly throughout the first half here against Juve. On the other side, nobody could stop ex-Atletico Madrid centre-forward Mandzukic in the air, with Ramos' strength and leadership really missed.

When the aggregate hit 3-3 with half an hour still to play, the Andalusian's joke after last week's game in Turin about getting his suspension out of the way before the semis did not seem so funny. Ramos will be back now for the semis, but Zidane will still need to find a way of stemming the issues down the flanks -- especially with Roma, Liverpool and Bayern Munich all featuring pacy wingers of their own.

This Madrid side always give you chances, they just always expect to score more of them than their opponents. Tonight, they left it very, very late, but they got there in the end.