For just the fourth time since the NHL lockout of 2004-05, the Stanley Cup Final will be decided by a Game 7. The series between the Boston Bruins and the St. Louis Blues has been partially defined by one team’s inability to direct shots at its opponent’s goal and the other team’s overpowering possession rate — but goaltending has been the real story.

Fortunately for the Bruins, goaltender Tuukka Rask’s playoff performance has been one of the best in recent history; unfortunately for the Blues, goaltender Jordan Binnington’s performance has been mediocre at best and ignominious at worst. Just how much less impressive Binnington has been than Rask in these playoffs is educational.

Now the Blues probably wouldn’t have qualified for the playoffs, let alone advanced to the Stanley Cup Final, without some exceptional regular-season goaltending from Binnington. When the rookie Bluenote claimed the No. 1 goalie position, the Blues had the worst record in the Western Conference. Binnington ended the season tied for the fourth-best save percentage, and won 24 of his 30 starts. And while his overall playoff performance hasn’t been one for the record books, Binnington has shown flashes of brilliance. (For example, Games 4, 5, and 6 of the Western Conference finals against the San Jose Sharks, when he stopped 75 of 77 shots faced, and Game 5 of the Stanley Cup Final, when he saved 38 of 39.) He just hasn’t been close to the same level as Rask.

Since the last championship-canceling lockout, Stanley Cup-winning goalies have averaged a Goals Saved Above Average (GSAA) of 5.30 in the playoffs, while Stanley Cup-losing goalies have finished with a GSAA of 4.51. Binngton’s GSAA for the 2019 playoffs has been -3.80, a mark that far underperforms both groups.

For his part, Rask has saved 15.29 goals above average in this year’s playoffs. Only one Stanley Cup goalie since the lockout has outperformed Boston’s netminder in terms of playoff GSAA: Tim Thomas, who saved an astounding 20.72 goals above average en route to winning the Stanley Cup with the Bruins in 2011. Rask has been better than 27 of 28 post-lockout Stanley Cup goaltenders in terms of GSAA, while Binnington has been worse than all but two of them.

We wrote recently that this series might be decided by whichever team’s goalie regressed less sharply. Both goalies have dropped off from the earlier rounds in terms of save percentage, which is normal in the Stanley Cup Final, and Binnington is the one who has regressed less sharply. But Binnington’s footing entering the final was less solid than Rask’s — Binnington’s save percentage entering the final was .914, compared to Rask’s .942. In the six games of the final so far, Rask is down to .925, while Binnington has dropped all the way to .901. This is critical because (I’m beating a dead horse, I know) save percentage accounts for a higher proportion of a team’s success than any other factor in hockey.

Rask’s performance in the first three rounds of the playoffs meant the Bruins wouldn’t suffer too badly if he took a few steps down into the basement. Rask has regressed, sure, but he had room to regress. The margin of error was more precarious for Binnington and the Blues, and unfortunately for fans in the Gateway City, their wunderkind is approaching the sub-basement. Binnington’s regression has hurt the Blues’ chances of winning their first-ever Cup.

In a way, Game 6 of the Stanley Cup Final was a microcosm of Binnington’s series. He was exceptional in Game 5 — it was his second-best game in terms of save percentage in the playoffs — and he made big save after big save in periods one and two of Game 6. But then period three happened, and Binnington gave up two savable goals he’d really prefer to have back.

On the other side of the ice, Rask made the saves that were expected of him — and a few saves that might prove iconic. Now the Cup hinges on a one-game series where the winner takes all. And in a series that’s been defined by goaltending, that could be bad news for the Blues.

CORRECTION (June 12, 2019, 10 a.m.): A previous version of the photo caption in this story misspelled the name of the Blues’ goalie. It is Jordan Binnington, not Jordan Billington.