For about 50 minutes, things looked dicey for the defending champions. Real Madrid had traveled to Naples with a fairly comfortable 3-1 aggregate lead over Napoli from the first leg of their Champions League round of 16. But by halftime, Real must have felt lucky to still be ahead.

The 11-time champions, seeking to become the first back-to-back victors in the Champions League era, were behind 1-0 and had seen goalscorer Dries Mertens knock another shot off the post. Had it gone in, the Neapolitans would have led the tie.

[ Follow FC Yahoo on social media: Twitter | Facebook | Tumblr ]

But a pair of Sergio Ramos headers, pushing the defender to a preposterous 71 career club goals – plus 10 more for Spain – put Real back ahead before the hour, and Alvaro Morata added an injury time goal, just to make a point. And so the second leg ended 3-1 as well. In the end, the 6-2 aggregate score looked much more convincing than it had really been.

Because 24 minutes in, Mertens – who is an attacking midfielder by trade but has been scoring by the bucketload since Napoli’s miracle worker-cum-manager Maurizio Sarri put him up front – was played through by Marek Hamsik. And the Belgian beat Real goalkeeper Keylor Navas with a tidy finish. That separated Napoli and the quarterfinals by just one goal, courtesy of its away tally three weeks earlier.

In the 29th minute, it seemed like Real would relieve some of the pressure it suddenly faced when Cristiano Ronaldo had a rare chance. He rounded goalkeeper Pepe Reina but somehow put his finish off the near post.

Real got away with a pair of chances around the 38th minute. First, Mertens pounced on a broken attack, the ball setting up beautifully for him at the edge of the box. He took a first-time whack without hesitating. It pinged off the bottom of the far post.

Then, Hamsik was dispatched on another of Napoli’s quick-trigger through balls, but the defense caught up to him and he was forced into a hurried long shot, which he sliced wide.

Still, Napoli had controlled the first half.

In the 51st minute, however, Ramos scored with his first headed goal off a corner. He got to the sharp corner by Toni Kroos and leaped above a pack of heads.

Six minutes later, he did much the same. Another corner. Another header. Only this time, Mertens tried to redirect it but wound up complicating his goalkeeper’s job.

The pair of away goals for Real put the tie beyond doubt, as Napoli now needed four goals in just over a half hour. So Zidane’s side slowed down the pace and consolidated its lead. The closest Napoli came after that was a pair of meek penalty claims by Mertens.

Real, meanwhile, added a third in the 91st minute, when substitute Morata smashed in a rebound from Ronaldo’s effort.

Real has now reached the quarterfinals seven years in a row. And in the last six, it reached the semis as well. The record-holders for European titles remain on track for a second in a row and a third in four years.

Leander Schaerlaeckens is a soccer columnist for Yahoo Sports. Follow him on Twitter @LeanderAlphabet.