Cristiano Ronaldo punished Paris Saint-Germain's slack defending once again, scoring a powerful second-half header as Real Madrid cruised into the Champions League quarterfinals with a 2-1 win on Tuesday.

Trailing 3-1 from the first leg, PSG's fragile defense crumbled and its attack offered little threat without the injured Neymar. The biggest bang from this PSG side was from the fireworks constantly let off by a section of fans behind one goal.

PSG's Dani Alves, left, holds Real Madrid's Cristiano Ronaldo during the round of 16, 2nd leg Champions League soccer match between Paris Saint-Germain and Real Madrid at the Parc des Princes Stadium in Paris, Tuesday, March 6, 2018. (AP Photo/Francois Mori)

Edinson Cavani's close-range goal gave PSG some hope with 20 minutes left. But with midfielder Marco Verratti already sent off, scoring two more to force extra time was beyond a lackluster PSG side.

Instead, midfielder Casemiro's deflected shot looped past stranded goalkeeper Alphonse Areola in the 80th to make it 5-2 on aggregate. He was gifted the ball after midfielder Adrien Rabiot dealt poorly with Lucas Vazquez's cross.

PSG's Angel Di Maria, second right, shoot on goal as Real Madrid's Varane, right, and Real Madrid goalkeeper Keylor Navas, defend during the Champions League round of sixteen second leg soccer match between Paris St. Germain and Real Madrid at the Parc des Princes stadium in Paris, France, Tuesday, March 6, 2018. (AP Photo/Christophe Ena)

To compound a miserable night for PSG fans, who so badly want to believe this side can conquer Europe, Verratti showed terrible composure to in getting sent off midway through the second half. He got a second yellow card, having protested vehemently with referee Felix Brych after not getting a free kick his way.

Ronaldo had already done his usual damage.

PSG's Edinson Cavani, left, tries to stop Real Madrid's Casemiro during the round of 16, 2nd leg Champions League soccer match between Paris Saint-Germain and Real Madrid at the Parc des Princes Stadium in Paris, Tuesday, March 6, 2018. (AP Photo/Francois Mori)

The Champions League's all-time leading scorer was given far too much space and leapt triumphantly to beat goalkeeper Alphonse Areola with a downward header in the 51st minute. It took his tournament-leading tally to 12, including two in the first leg.

After a slow start this season, Ronaldo is hitting top form at a crucial time for a Madrid side looking to win the competition for the third straight time and 13th overall. He has scored in nine Champions League games in a row, matching Ruud van Nistelrooy's record.

Real Madrid's Cristiano Ronaldo reacts after scoring the opening goal of his team during the round of 16, 2nd leg Champions League soccer match between Paris Saint-Germain and Real Madrid at the Parc des Princes Stadium in Paris, Tuesday, March 6, 2018. (AP Photo/Francois Mori)

This was a huge test for a PSG side desperate to prove it belongs among Europe's elite, especially after spectacularly failing last year — becoming the first team eliminated after winning the first leg 4-0. Barcelona won the return 6-1.

This time, there was simply not enough belief shown and too many sloppy mistakes.

Real Madrid's Sergio Ramos jumps in the arms of Real Madrid's Lucas Vazquez, left, as Real Madrid's Casemiro, right, joins in celebrating scoring their side's first goal during the Champions League round of sixteen second leg soccer match between Paris St. Germain and Real Madrid at the Parc des Princes stadium in Paris, France, Tuesday, March 6, 2018. (AP Photo/Christophe Ena)

Liverpool held 0-0 by Porto, into Champions League quarters

Liverpool relied on its five goals from the first leg to oust Porto in the last 16 of the Champions League as the teams played out a dull 0-0 draw in the return match on Tuesday.

Protecting a 5-0 lead, Liverpool manager Juergen Klopp had the luxury of resting the joint-top scorer in the Premier League — Mo Salah — and world's most expensive defender — Virgil van Dijk — for the second leg at Anfield.

The English team didn't need to exert itself to secure a place in the quarterfinals of European soccer's top competition for the first time since 2009, though came close to another victory with Sadio Mane striking a first-half shot against the post.

Liverpool's Dejan Lovren, center, attempts a header at goal during the Champions League round of 16, second leg, soccer match between Liverpool and FC Porto at Anfield Stadium, Liverpool, England, Tuesday March 6, 2018. (AP Photo/Dave Thompson)

For a club with Liverpool's European prestige and history, nine years out of the Champions League's last eight is some wait. The five-time European champions return as the competition's top scorers this season with 28 goals and will be feared by the other qualifiers ahead of the March 16 draw for the quarterfinals.

Also in the draw will be Real Madrid, which beat Paris Saint-Germain 2-1 away to clinch a 5-2 aggregate win in the marquee matchup in the round of 16. Cristiano Ronaldo was one of the scorers for Madrid, the Portugal forward netting for the ninth straight game in the Champions League.

A year ago this week, Barcelona became the first team to overturn a 4-0 first-leg deficit in the Champions League knockout stage when beating PSG 6-1.

Liverpool coach Jurgen Klopp talks with the fourth official, right, during the Champions League round of 16, second leg, soccer match between Liverpool and FC Porto at Anfield Stadium, Liverpool, England, Tuesday March 6, 2018. (AP Photo/Dave Thompson)

Porto, the Portuguese league leader, had to go one better but Klopp's decision to field a strong team rendered that unlikely scenario even more inconceivable.

Those fringe players that did come in for Liverpool — Adam Lallana and Alberto Moreno being two of them — had the carrot of staking a claim for a place in the team for Saturday's big Premier League match against Manchester United.

Liverpool's Sadio Mane, right, attempts a shot at goal during the Champions League round of 16, second leg, soccer match between Liverpool and FC Porto at Anfield Stadium, Liverpool, England, Tuesday March 6, 2018. (AP Photo/Dave Thompson)

And it was the hosts who had the better of the chances, with Mane hooking a volley over the bar and then striking a low shot against the post in a subdued first half.

Roberto Firmino ran clear but ended up having a shot blocked on the hour, before immediately being taken off by Klopp as Liverpool's main striker was protected ahead of the United game.

Porto pressed late on but to no avail, as it failed to collect a first away win over an English opponent in the Champions League at the 13th attempt.