The 2019 Mid-Season Invitational G2 vs SKT Semifinals on top of the list with a peak view of 1,704,326.
On the 10th of June, Esports Charts - an analytical agency that specializes in collecting esports information - revealed an interesting statistic on "the most popular esports tournaments in May".
The above is a statistic on the tournaments that had the highest peak views in May. Chinese platform users haven't been included in this analysis.
According to their monthly report, the 2019 Mid-Season Invitational (MSI) has made it on top of the list, peaking up to a total of 1,704,326 views. Although it shows that the SKT vs G2 Semifinals was the most popular series, the numbers could have been higher with Esports Charts stating that the stats for the 2019 MSI Finals hasn't been updated.
With Dota 2 - MDL Disneyland® Paris Major on 2nd place, mobile game, Arena of Glory's Spring season made in on 3rd. Counter-Strike: Global Offensive - IEM Sydney and Overwatch League: Stage 2 followed.
Information and Image from Esports Charts