Team Secret and Vici Gaming got off to undefeated starts Thursday in the first day of group stage play at the International 19 in Shanghai, China.
Team Secret sits atop Group A at 6-0, while Vici Gaming leads Group B at 4-0.
PSG.LGD also had a good day, finishing 5-1 and in second place in Group A. Virtus.pro and OG are tied for second in Group B with 3-1 records.
The 18 teams are divided between two groups and playing a round-robin, best-of-two format. The top four teams in each group will advance to the Upper Bracket of the Main Event, the bottom team in each group is eliminated, and the remaining teams will participate in the Lower Bracket of the Main Event.
The teams are vying for a record prize pool of more than $33 million, with the winning team to take home more than $15 million.
On Thursday, Team Secret swept Team Liquid to move to 6-0. That followed sweeps of Newbee and Alliance.
Vici Gaming won its series against Royal Never Give Up and Fnatic. RNG gave Vici Gaming a tough first contest, with VG squeezing out a win, but VG didn't face a serious challenge after that, topping RNG in their second battle, then defeating Fnatic 2-0.
Fnatic pulled off an upset by sweeping Evil Geniuses, who were expected to compete for the title.
Evil Geniuses salvaged a split against Natus Vincere, dropping the first game but coming back to win the second game that lasted 82 minutes.
PSG.LGD dropped just one game on the day. After sweeping Keen Gaming and Chaos Esports Club, PSG.LGD dropped its first game against TNC Predator, then came back to take a win. TNC is in third place in Group A after Day 1, with Chaos in last place.
In Group B, Virtus.pro played a pair of tight matches, defeating Ninjas in Pyjamas 2-0. Against RNG, Virtus.pro split the match to move to 3-1.
Tied with Virtus.pro, OG swept Infamous and split with Natus Vincere.
The Main Event is set for Aug. 20-25 at Mercedes-Benz Arena.