And then there were eight. The Champions League field has once again been whittled down, with a rousing round of comebacks and surprises leaving some of Europe's marquee clubs - including the three-time reigning champions - by the wayside. Heading into the quarterfinals, there looks to be a clear divide between the four tournament favorites and the quartet of underdogs enjoying unlikely runs. Here's how the remaining teams stack up.
How they got here: 4-3 aggregate win over Roma
As harsh as it sounds, Porto is the team everybody else in the competition will be hoping to draw when the quarterfinal matchups are revealed on Friday.
That won't quell the enthusiasm of manager Sergio Conceicao, though. In a campaign defined by enthralling upsets thus far, the 44-year-old bench boss - whose reputation continues to grow rapidly - boasts an underrated squad that combines in-demand youngsters with a group of grizzled veterans who are no strangers to the latter stages of Europe's showpiece competition.
Nowhere is that more apparent than in defense, where 21-year-old Eder Militao slots in alongside 36-year-old Pepe; the former is on his way to Real Madrid after Los Blancos agreed to pay his €50-million release clause, while the latter won three Champions League titles at the Bernabeu during his decorated spell in the Spanish capital.
Up front, Moussa Marega spearheads an attack that's been ruthless at the Estadio do Dragao this season. Porto have won all four of their home matches in the tournament thus far, outscoring opponents 11-3 in the process. The competition level hasn't been overly difficult - Porto emerged from a weak Group D - but the comforts of home cooking are evident.
Only Lionel Messi and Robert Lewandowski have scored more goals in this season's Champions League than Marega, whose swift return from a thigh injury sparked Porto's tense extra-time victory over Roma.
How they got here: 3-3 on aggregate vs. PSG (won on away goals)
There are still plenty of questions about Ole Gunnar Solskjaer's long-term viability as Manchester United manager, but good luck trying to convince both Red Devils fans and players that he doesn't deserve the gig right now.
Yes, there was an element of luck involved in United's stunning win over Paris Saint-Germain - two horrendous individual errors from the Parisian side and a contentious penalty in the dying minutes, to be precise - but there's no denying that the Norwegian gaffer has restored some vital intangibles to a team that was withering away under Jose Mourinho.
He's getting the best out of superstar midfielder Paul Pogba and has instilled a sense of belief that was simply non-existent prior to his arrival. Are those enough to carry a team to a Champions League title? Considering the sheer quality, both technically and tactically, of the other remaining sides, probably not, but it makes United a dangerous team to write off.
If anybody knows about overcoming seemingly impossible odds to hoist the coveted big-eared trophy, it's Solskjaer.
How they got here: 4-0 aggregate win over Borussia Dortmund
Don't sleep on Tottenham.
Their title push may have come to a screeching halt domestically - Spurs have been dragged back into the four-team dogfight for England's final two Champions League slots - but on the continent, they're coming off the back of a wholly impressive victory over Borussia Dortmund that showcased all the hallmarks of a team capable of reaching the semifinals.
They flipped the switch late in their first-leg encounter against BVB, using a second-half blitz to bury the previously high-flying German side, and then defended their advantage resolutely in the return fixture, getting a clinical goal from Harry Kane on their only real opportunity of the match.
Mauricio Pochettino's side has, by and large, weathered the injury storm that hit them early in 2019, with Dele Alli's return offering an enormous boost for a club that didn't have another player capable of replicating the 22-year-old's unique skill set.
Questions remain in midfield, but with their core group all fit once again, Tottenham will offer a tricky test for any of the proverbial powers remaining in the competition.
How they got here: 5-3 aggregate win over Real Madrid
Last call to hop on the best bandwagon in town.
Responsible for the most exhilarating result of the last 16, Ajax enter the quarterfinals riding a wave of enthusiasm - and support from neutrals everywhere, no doubt - after their relentless pressing and high-octane attack tore an overwhelmed Real Madrid to shreds at the Santiago Bernabeu.
All the hallmarks of Johan Cruyff's legendary footballing philosophy were on display, carried out by the typical collection of blossoming youngsters - Frenkie de Jong, Matthijs de Ligt, David Neres, and Hakim Ziyech chief among them.
But it was a reinvigorated veteran who served as the lynchpin.
Dusan Tadic, the 30-year-old who was discarded last summer by Southampton, has been the focal point for the Dutch club this season. A wizard with the ball at his feet - just ask Casemiro, who's still spinning after trying to curtail the Serbian midfielder - Tadic's performance in the second leg in Madrid will go down as one of the best of the competition.
Another showing like that and Ajax could be in line for their first appearance in the semifinals since 1997.
How they got here: 3-2 aggregate win over Atletico Madrid
Turin is still buzzing.
After months of playing with the handbrake on and doing barely enough to get by, a memorable Tuesday evening saw everything finally come together for Juventus. Massimiliano Allegri drew up a fantastic game plan; Emre Can, playing a flexible, unfamiliar role, had his best match since joining the club; Federico Bernardeschi, starting in place of beloved No. 10 Paulo Dybala, was unstoppable; and, of course, Cristiano Ronaldo showed exactly why the Italian giants splashed €100 million to acquire him.
A hat-trick from the Portuguese gave Juve the 3-0 win they needed to overcome their daunting first-leg deficit against Atletico Madrid, and the final whistle brought with it a sense that, at long last, we finally got to see what this side is capable of when Juventus really decide to push the pedal to the floor.
Which Old Lady will we see for the remainder of this tournament?
If we get the one that cowered last month in Madrid, their scintillating comeback will be nothing more than a footnote. If, however, they use Tuesday's ferocious win as a springboard, Juve may finally be able to end their Champions League drought and satiate their obsessive desire to capture this prize for the first time since 1996.
How they got here: 3-1 aggregate win over Bayern Munich
So, still think Liverpool can't deal with the pressure?
Questions have been asked of the Reds' title credentials in recent weeks, as they have agonizingly watched Manchester City haul them in - and ultimately leapfrog them - in the race for the Premier League crown. But Jurgen Klopp's side made a statement on Wednesday in Bavaria, strolling into one of the great bastions of European football and walking away with an altogether comfortable win over Bayern Munich.
Mohamed Salah has scored just once in his last nine matches across all competitions, but the electrifying Sadio Mane is picking up the slack, while Virgil van Dijk continues to justify every last penny of his £75-million transfer fee. At this point, the towering Dutchman looks like a bargain, if anything.
Armed with a more sustainable style of play this season - Klopp has let up somewhat with his gegenpressing approach - Liverpool won't fear anyone heading into Friday's quarterfinal draw.
How they got here: 5-1 aggregate win over Lyon
With perennial semifinalists Real Madrid and Bayern Munich both sent packing early this season, the era of the "big three" in the Champions League seems to finally be on the wane. The balance of power feels like it's shifting.
But while the past two tumultuous weeks have felt like a watershed moment in European football on a club level, this still remains, without question, an era defined by the individual genius of Lionel Messi. He alone ensured that Barcelona, the third and final member of the Champions League's long infallible trio, didn't suffer a similar fate to their two gargantuan peers.
There were some nervy moments in the last-16 tie against a valiant Lyon side capable of exploiting space on the counterattack, but once the Argentine decided to take matters into his own hands, Barca's place in the quarterfinals was secure. Messi scored twice and set up two more at the Camp Nou on Wednesday, combining nonchalant scoring prowess with a passing repertoire that makes onlookers weak in the knees.
The age of Real Madrid and Bayern dominance is over, but Messi remains.
How they got here: 10-2 aggregate win over Schalke
The new European superpower?
Manchester City, ultimately, made light work of an overmatched Schalke side to book their place in the quarterfinals, running roughshod over the German side's porous backline en route to a 7-0 victory in the second leg. Late goals from substitutes Phil Foden and Gabriel Jesus, slick as they both were, just felt cruel. For all the upsets the tournament tossed our way, this was a stark reminder that City, flush with cash, talent, and arguably the world's most revered tactical mind, look poised to assume the mantle atop Europe.
The attacking might of Pep Guardiola's shape-shifting outfit is staggering; they create opportunities with ease and have the individual stars capable of breaking matches open on the rare occasions the systematic approach to scoring goals hits a snag.
With the likes of Real Madrid, Bayern Munich, and PSG already out of the competition, this is City's best chance yet to deliver the title the club's ownership group so desperately craves.