We're over halfway through the BLAST Premier Spring Series, and, after an incredibly eventful opening weekend, it was difficult to imagine anything that could top FaZe Clan's dominant run in Group A.

But Week 2 of BLAST upped the ante, producing some of the biggest upsets in the tournament's history.

Underdogs Complexity stunned world No. 1 Astralis in their opening game before pulling off another shock victory against Team Vitality to reach the Spring Finals.

Na'Vi did the uneasy job and ended Complexity's unlikely crusade with victory in the final game, with both teams joining FaZe and Team Liquid at the finals in June.

With plenty to unpack from Group B, here are some of the things we learned from Week 2.

What's going on with Astralis?

Astralis had a particularly bad day at the office: the last time the team finished in last place at an event was in the inaugural finals of ECS back in 2016. BLAST

Astralis were the heavy favourites going into the entire tournament, never mind this weekend. But the veteran front runners suffered a shock 2-0 defeat to a fresh-faced Complexity roster -- a side widely considered to be the underdogs of Group B.

They picked themselves back up in the losers' bracket and dominated Na'Vi on Train but failed to find the edge to secure a win and were subsequently relegated to the Spring Showdown after losing the second and third maps.

Make no mistake, losing in this fashion will be a distant feeling for many in the Astralis roster --the last time the team finished in last place at an event was in the inaugural finals of ECS back in 2016. So, how did a four-time Major winning side fall flat after finishing 2019 on such a high?

Nicolai "dev1ce"Reedtz said there were some communication issues during the match against Complexity that contributed to their loss.

"A lot of things went wrong," dev1ce said. "It was the first game of the year so it's hard to pinpoint exactly what went wrong. There's a lot of things in game and also communication and preparation so I guess you have to mix that with Complexity playing well and it being an off day.

"Sometimes when we lost the first kill the communication just died, it doesn't really happen that often. What happens is we just run into them instead of resetting and talking about what to do next.

"It's something we've abused with some of the other teams so it's quite stupid that we fell into that trap of not speaking. It's been a while since we played our last game on stage so we just have to get back into it."

Other teams have their own theories as to why Astralis underperformed.

Oleksandr "s1mple" Kostyliev said that both Na'Vi and Complexity having already competed this year gave them an advantage over Astralis.

"The teams Astralis played already felt their own games," s1mple said. "For example, Complexity already played online qualifiers for the Major, we played in the ICE challenge and we had time to try and find our game.

"Astralis came into the new season and nobody really knew what to expect from them and because of this, maybe they didn't have enough time to find their game yet."

Despite the poor results, Astralis' dev1ce admitted there are positives to take away from the tournament.

"It was a good thing that we didn't get angry with each other," dev1ce added. "That's something we're pretty good at, just staying cool and calm and trying to work out our mistakes.

"There wasn't that many positives but you still have to look at the experience as something you can learn from and something you can improve on. In the start of the year, there are a lot of things you can work on a lot of the times so it's just about picking up what matters for us."

Astralis also had a slow start in the first half of 2019, but they managed to overcome their issues and win two majors. But, with IEM Katowice on the horizon, there's certainly no need for Astralis fans to panic just yet.

Don't underestimate Complexity

Complexity pulled off shock victories over Astralis and Team Vitality to reach the Spring Finals in June. BLAST

On paper, Complexity were arguably the weakest team in a group that consisted of world class players such as dev1ce, ZywOo and s1mple.

Led by Benjamin "blameF" Bremer and coach Jamie "Keita" Hall, some of the roster have never even faced the likes of Astralis and Team Vitality at LAN events, making their victories that bit more impressive.

It's easy to focus on Astralis' underwhelming performance and forget just how impressive their opponents were: Complexity have only played together for a month.

"The offseason was a little up and down," blameF said. "We're a new team so we definitely had some trouble making it all work. I think it would have been easier if we knew what kind of weaknesses we have but because we're new, we had to spend a lot of time to identify what those weaknesses are and then try to fix them.

"We have played a lot over the last month and have spent a lot of time getting to know each other but one month in Counterstrike isn't that much."

Their impressive display attracted the attention of their challengers, in particularly dev1ce, who was full of praise for Valentin "poizon" Vasilev.

"Complexity have five good players and they played well but in our match, poizon definitely was the one with the most impact," dev1ce said. "It's hard to see sometimes for spectators but some of the opening kills and some of the map rotations and control he had alone was really important.

"He was the guy I was most surprised with, poizon was the MVP of that game for me, by far."

Although Complexity eventually fell to Na'Vi in the upper bracket final, they once again managed to impress their opposition.

"They had a lot of courage," Na'vi's coach Andrey "B1ad3" Gorodenskiy said after beating Complexity. "The thing that impressed me was that they never gave up. They were trying to always find an idea with how to play and didn't get tilted.

"However, I still think there's a lot of weaknesses in their play. They're a team with good potential but I don't think they're a top ten team yet. At this point, they have very skilled players who are stars in the team but they must become a star team, not just a team of star players."

A star is born

Complexity's 16-year-old lurker Owen "oBo" Schlatter showed superb skill to take down world No. 1 Astralis, despite being the youngest player in the tournament. BLAST

As B1ad3 said, this Complexity roster already had some stand out players, but a star was born in the shape of 16-year-old Owen "oBo" Schlatter.

The Complexity lurker is the youngest player in the tournament and, despite not being the best fragger on his side this weekend, oBo shined on the London stage.

Snagging 45 kills against Astralis, oBo was exceptional on Dust II and Vertigo, and he kept his cool in clutch moments -- a vital attribute to have that can often make a difference between winning and losing.

"For some reason, I felt really confident," oBo said. "In the beginning I was a little nervous but once I started playing, all the nerves were gone and I was just happy to be doing my thing."

"It means the world to me that I managed to beat some of the players I've looked up to my entire Counterstrike career.

"If you told a year ago I'd be beating Astralis, I wouldn't have believed it. I'm just so proud of my team."

His teammate blameF has high hopes and expectations for the youngster and believes the investment in oBo will benefit Complexity in the long run.

"I'd say he's definitely a wildcard," blameF added. "He's definitely the guy that wins us the most rounds but he's also the guy that loses us the most rounds so he has a lot of time to grow.

"There's a lot of stuff he doesn't know about Counterstrike because he hasn't been playing professionally for that long so he's just lacking in experience. But I'd say he'll be a big star in the future and I hope he'll become one of our brothers and stay with us for a very long time.

"He's a really big star, he works really hard and takes in criticism so it's more about him just learning all the aspects of what Counterstrike has to offer."

Which team looked the strongest?

World No. 1 Astralis suffered a shock defeat at the hands of Complexity, before losing again to be relegated to the Spring Showdown. BLAST

B1ad3 confidently said that Na'Vi were the best team this weekend. He's not wrong.

Despite losing to Team Vitality in their first game, they came back stronger and stronger and became an unstoppable force by the time they reached the upper bracket final, even though Na'Vi were playing less than 24 hours after competing in the finals of the ICE .

"We're the best team here this weekend," B1ad3 said. "It's obvious. We beat every team here.

"Of course, if we had to play Astralis, I'd say they could beat us because we got a bit lucky against them when we beat them. We know there are a lot of teams in the world that can beat us so we need to work harder.

"We're not delusional about our position in ranking and so on -- we just know our potential."

Indeed, Na'Vi showed more than just potential, especially with their convincing, consistent victories over Team Vitality and Complexity.

They will join FaZe Clan, Team Liquid and Complexity in the Spring Finals in June, and it's not out the question that Astralis and Team Vitality can claw their way back into form by then.