The format of the group stage was two groups of eight teams in a double elimination bracket. The teams to win their brackets moved on to the semifinals while the next two teams were in the quarterfinals.
Group A Winner's bracket Astralis came in as the best team in the world and proved its dominance by easily handling ENCE eSports. Cloud9 had Martin "STYKO" Styk come in as a stand-in as the team struggled to find a permanent replacement for Pujan "FNS" Mehta and after STYKO was removed from the mousesports active lineup. Although STYKO struggled somewhat, Cloud9 had no problem taking care of Ninjas in Pyjamas, as the Swedes had only a few highlights in the game. mousesports also had a new player on the team after replacing STYKO with Janusz "Snax" Pogorzelski, as Snax left the legendary Polish squad
Virtus.pro. However, mousesports did not need Snax to shine as mousesports easily took down Gambit Esports. In the first upset of the day, G2 Esports took down the rising Natus Vincere in a very close match as the French were able to overcome a 9–0 deficit as
Edouard "SmithZz" Dubourdeaux shined. In the first best of three, Astralis was able to stifle a Cloud9 comeback on the first map and then erased all hopes in the second map with a 16–1 win as Nicolai "dev1ce" Reedtz dominated the field. G2 continued to crawl its way through the winner's bracket as
Kenny "kennyS" Schrub showed why he was considered the best AWPer one time. Both G2 and Astralis secures spots in the playoffs. In the loser's bracket, ENCE pulled off a massive upset as
Aleksi "allu" Jalli was able to completely thrash his former team and the Ninjas in Pyjamas were eliminated. Gambit had the unfortunate luck to run into a top three team in the first round of loser's as Gambit could do nothing to stop the power of Oleksandr "s1mple" Kostyliev, who many are calling the world's best player. Gambit was eliminated. ENCE somehow managed to pull off an even bigger upset against mousesports by sweeping the decorated European squad in two close maps as allu took revenge on another one of his former teams. Natus Vincere and Cloud9 were also part of a very close series, but it was s1mple to outduel Timothy "" Ta to eliminate Cloud9. In the winner's finals match, G2 made a massive comeback against the world's best, but Astralis was able to take the map into overtime. Astralis took that small wave of momentum into the next map and finished off G2 with ease to guarantee a spot in the semifinals. ENCE continued its
Cinderella story as it took the first map against Na'Vi. In the second map, Na'Vi looked to easily take it, but Jere "sergej" Salo was rolling as ENCE started to make a comeback; however, Na'Vi was bailed out by s1mple and Denis "electronic" Sharipov and Na'Vi scraped by and then easily took the third map to move on to the playoffs.
Group B Winner's bracket FaZe kicked off group B with a closer-than-expected match against B.O.O.T-dream[S]cape. The two top five players on FaZe, Nikola "NiKo" Kovač and Håvard "rain" Nygaard, were able to carry their team to an easy terrorist side to send the team from Singapore to the loser's bracket. mibr made its Global Offensive debut after signing one of CS:GO's most successful cores, but the legendary Brazilian brand struggled against the Noah "Nifty" Francis-lead Renegades. However,
Gabriel "FalleN" Toledo's team showed signs of its old self: making improbable comebacks. Despite Renegades's 6–0 start and 10–5 halftime score, Marcelo "coldzera" David and Fernando "fer" Alvarenga showed why they were ranked as the best and third best players in 2017. Fnatic vs. North showcased two teams who had been struggling. Fnatic started out strong, but North winning five rounds in a row to start the second half suddenly made the game close. In the end, Fnatic was able to clutch out the 30th round to advance in the winner's bracket as Jesper "JW" Wecksell showed signs of the 2015 Fnatic days. BIG seemed eager to play in front of its home crowd and after picking up Owen "smooya" Butterfield, the team showed rapid paces of improvement. This showed in the match against Team Liquid, North America's best team as BIG was able to completely run over Liquid's defense. Although Jonathan "EliGE" Jablonowski topped the scoreboard out of all the ten players, the rest of his Liquid teammates struggled. After having never beaten any of FalleN's teams in his career,
Finn "karrigan" Andersen found his second series win in a row in two relatively close maps as surprisingly karrigan topped the scoreboard over his superstars. In the other winner's match, Fnatic was able streak away with the series win after a close first half on the first map as the Swedes advance to the playoffs. In the loser's side, Renegades made quick work of B.O.O.T-dream[S]cape and eliminated the Singaporeans. Team Liquid struggled heavily at the event after falling to the declining North, even after a solid third-place finish at ESL One Belo Horizonte and a second-place finish at ECS Season 5. However, the American team fell to Mathias "MSL" Lauridsen's team and was ultimately eliminated. In a very tense best of three, it was the Australians and the Germans to provide the best series of the group stage. Renegades and BIG took one map each, but the third map was a toss-up. In the end BIG to end up on top in overtime behind Johannes "" Wodarz's 31 kills. Although not as exciting, North and mibr played a close best of three that went all three maps, but it was the star dup of fer and to outduel Valdemar "valde" Bjørn Vangså and North was eliminated. In the maps they won, the players of FaZe completely dominated Fnatic. The Swedes were able to take a map, but the result was not close. The final decider match ended up being a thriller. BIG and were able to split the first two maps at the same score. The third map went to double overtime and mibr looked to take it. However, BIG was able to shut down mibr's offense and BIG would face G2 Esports in front of its home crowd. With 's exit, the two-time defending champions of ESL One Cologne was out of the tournament. ==Playoffs==