What exactly did the St. Louis Blues do to win 4 games against the Chicago Blackhawks? Taking a look at the dataviz below you see how St. Louis compared to Chicago in some key metrics. Corsi? Chicago. Scoring Chances? Chicago. Save percentage? Chicago. Where did St. Louis beat Chicago? High danger scoring chances. The Blues had more high scoring chances than Chicago did at 5v5 and out of all the scoring chances the Blues' attempted, most of them were high scoring (and their ratio was better than Chicago's). St. Louis also had a better on ice shooting percentage than Chicago as well.
Compare how the Blues' and Blackhawks' matched up against one another during the regular season in regards to their high danger scoring chance rates both for and against. When playing each other in the regular season, the Blues had above league average HSCF/60 and below league average HSCA/60. Meanwhile, the Blackhawks' high danger scoring chances, both for and against, were on the wrong side of league average when playing the Blues. It only got better for the Blues in the playoffs. They were able to generate high danger scoring chances at a greater rater against Chicago during the first round than they did during their regular season games against Chicago.
You can take a look at the shot map underneath the dataviz and you can see for yourself the density of the shots for the Blues that fall inside the dotted line "arrowhead" area that is the high danger area on the ice. Then look at the Blackhawk's shot map. Not nearly as dense in the high danger area.
If high danger scoring chances is how the Blues beat the Blackhawks, will the same strategy work on the Dallas Stars? The chart at the bottom of the second tab of the dataviz shows regular season high danger scoring chances for per 60 versus high scoring danger chances against per 60. Dallas was the outlier this season amongst playoff teams. They had both the highest HSCF/60 and the highest HSCA/60. This is with a goaltending duo who has one goaltender above league average for high danger save percentage (Niemi) and another goaltender with below league average high danger save percentage (Lehtonen). The Blues are in the "sweet spot" with above average HSCF/60 and below league average for HSCA/60. Elliott also had the 2nd best high danger save percentage at 5v5 for regular season (Niemi is 13th).
I'm not a fan of just using one stat to determine the fate of a team, but the high danger scoring chances is the one stat that the Blues beat the Blackhawks at during the first round. If they continue generating these high danger scoring chances against the Dallas Stars at the same rate they did against the Blackhawks, the Blues might just find themselves playing in the conference finals this year.