3 things you need to know about Tuesday's Champions League action

The first matchday of the Champions League featured half of Europe's biggest clubs, all eager to start their European campaigns with three points. Cristiano Ronaldo and Gareth Bale led the Real Madrid attack to a 5-1 drubbing of Basel, while last year's runner-up Atletico Madrid were dealt a shocking loss at the hands of Greek giants Olympiacos and Liverpool narrowly avoided humiliation against Bulgarian Cinderella side Ludogorets Razgrad.

theScore's Gord Brunt and Carlo Campo run down three things you need to know from Tuesday's Champions League action.

Last season's finalists experience divergent debuts

Gord Brunt: Diego Simeone's men were left with their heads in their hands as Atletico Madrid came short of a stunning comeback against Olympiacos, dropping their opening match of the Champions League.

Before Atletico Madrid could adjust to the intense atmosphere at the Karaiskakis Stadium in Athens, the reigning La Liga champions found themselves down 2-0 inside the first half hour of the match. A valiant effort from the visitors halved the lead shortly before halftime, but Kostas Mitroglou's 79th-minute strike cancelled out Antoine Griezmann's goal to give the Greeks a crucial 3-2 victory.

Real Madrid, on the other hand, made easy work of Basel as the Spanish club began its quest to capture an 11th European title.

The game was essentially over after 37 minutes when James Rodriguez gave the hosts an insurmountable 4-0 lead over the Swiss club, but it will be Gareth Bale's goal on 30 minutes that will leave fans buzzing about the Welshman's otherworldly talents.

Carlo Campo: Although Atletico Madrid emerged with a 2-1 win over Real Madrid in last weekend's Derbi Madrileno, it was Los Galacticos who got their Champions League campaign off to a better start on Tuesday.

Atleti aren't the type to give up three goals in a single match, but their 3-2 loss to Olympiacos means they've already conceded the same number of goals as they did throughout the entire group stage of last season's Champions League.

Uncharacteristic sloppiness from Atleti's backline was to blame for two of the Greek side's three goals, and it unfortunately rendered their tactic of attacking down the flanks useless. Note that both Mario Mandzukic's header and Antoine Griezmann's composed finish were the result of accurate crosses, which Atleti consistently delivered over the course of 90 minutes.

Real Madrid, on the other hand, have plenty to celebrate following their 5-1 trashing of Basel.

In a match where Karim Benzema notched Los Galacticos' 1000th goal in European competition, Cristiano Ronaldo scored his 68th Champions League goal to stand alone as the competition's second all-time scorer. Raul currently holds the record with 71.

Furthermore, the five-goal performance means that Carlo Ancelotti has watched his side score at least three goals in nine of their 14 Champions League fixtures.

Whether Real Madrid were phenomenal or Basel were terrible is up for debate, but there's no arguing that Gareth Bale scored the most impressive goal of the night. In something of a throwback to the 2011-12 Tottenham lineup, he finished off a precision-perfect through ball from Luka Modric.

Borussia Dortmund completely overwhelm Arsenal

GB: It was a flattering scoreline for Arsenal during their opening match against Borussia Dortmund, as the Germans could have easily won by a touchdown if it wasn't for some lack of finish by their collection of talented attackers.

The English side failed to register a shot on target by the time Dortmund slotted one past the Arsenal 'keeper, seconds before halftime. The Germans unleashed 15 shots (four on target) in the opening 45 minutes and didn't let up when the second half began. Pierre-Emerick Aubameyang's goal three minutes after the break would prove too much for Arsenal to overcome. 

Arsenal couldn't seem to adjust to Dortmund's suffocating attack, as they continually lost one-on-one battles and conceded possession on too many occasions to remain competitive. Meanwhile, Dortmund's fluidity and lethal finishing could take them to the knockout round as group winner for a second consecutive season.

CC: Dortmund had 24 total attempts. Arsenal had four. Dortmund registered seven shots on target. Arsenal registered one. Oh, and let's not forget about this little gem.

In a far more one-sided affair than most people could have anticipated, Jurgen Klopp's side completely overran the Gunners and were unlucky not to win by more than two goals.

Arsenal have now conceded at least two goals for the 11th time in their last 19 Champions League fixtures, and while it's easy to pin the blame on the club's injury woes in their backline, Dortmund's injury situation is arguably just as bad - they're currently without Marco Reus, Jakub Blaszczykowski, and Nuri Sahin.

Here's a statistic for the Arsenal supporters who have over-the-top expectations for their side in Europe:

Liverpool avoids shocking result against Ludogorets Razgrad

GB: Ludogorets Razgrad, playing in their first ever Champions League match, were minutes away from leaving Anfield with a famous point. Then a soft penalty decision during stoppage time denied the Bulgarians an upset of Liverpool.

Dani Abalo sent the visitors into a frenzy when his 90th minute goal cancelled out Mario Balotelli's first appearance on the scoresheet as a Liverpool player. 

The joy was short-lived, however, as Javi Manquillo's drive into the Ludogorets box forced 'keeper Milan Borjan to come out and challenge, leading to a questionable foul call and a Liverpool penalty. Steven Gerrard, as he's done so many times before, calmly launched the Merseyside club to three points in their first Champions League match since 2009.

CC: Was this worthy of a penalty? You be the judge.

[Courtesy: Reddit user "FifthMistake"]

If you enjoy rooting for the underdog, you'll probably agree that Javi Manquillo went down far too easily and that Liverpool didn't deserve to squeak out a 2-1 win against Ludogorets.

The dramatic finish at Anfield was a cruel ending for the Bulgarian side, who deserved at least a point as they continually threatened Liverpool for chunks of the match (particularly in the second half).

If you agree with the penalty instead, Abalo's heartwarming celebration of his 91st-minute equalizer with a disabled supporter will surely change your mind.