The Houston Astros and Washington Nationals will play World Series Game 4 on Saturday night. The Nationals go in with a 2-1 lead in the best-of-seven series, but the Astros are coming off a Game 3 victory. This is baseball, a sport built to defy assumptions, but it says here that whoever takes Game 4 will (probably) win the entire series. 

From the Nationals' standpoint, this isn't a particularly bold thing to say. A Game 4 win behind starter Patrick Corbin would mean they'd have a 3-1 series lead and be tasked with winning only one more game before the Astros win three more. Throughout history, teams in the Nationals' hypothetical position -- i.e., up 3-1 in a best-of-seven without home field advantage -- have gone on to win the series in question 83.8 percent of the time. Stated another way, of the 37 teams to go up 3-1 without home field advantage, just six have lost that series. If the Nats win at home on Saturday night, they become overwhelming favorites to win the World Series for the first time in franchise history. 

Now consider the Astros. They lost Games 1 and 2 at home before bouncing back on the road in Game 3. Coming out of the Houston games, the Nats were in complete command, but the Friday win behind strong relief and timely hitting put the Astros back in it. A win in Game 4 would erase that surprising 2-0 lead that the Nationals built, and in essence it would make this series a best-of-three with the Astros once again holding home field advantage. 

That in some ways means a reset. The rotations turn over after Game 4. The mentalities would be different. The Nationals would know they're no longer able to win the World Series at home and know that the lead they built had been squandered. The Astros, meantime, would get back to the starting line as the heavy favorites. Look at regular season, look at run differential, look at batted ball outcomes, and the Astros are the superior team. That's the case even if you throw out the Nationals' results prior to May 23, when they were a season-worst 12 games under .500. Sure, you can assume the Nationals found their level after that low point, but the Astros were still the better team even when you use that Nationals-friendly end point. 

If the Astros achieve that rest and it becomes a best-of-three, then the Nats will likely face a full-rest Gerrit Cole in Game 5 and then an extra-rest Justin Verlander in Game 6. A Game 7 would probably mean an all-hands-on-deck pitching approach for both teams, but a full-rest Zack Greinke plus the Astros' superior bullpen depth would give them an edge on paper. 

Coming into the series, bookmakers had the Astros as roughly a two-to-one favorite, and the SportsLine Projection Model (@SportsLine on Twitter) was even a little more bullish on Houston. Given that this would be a new series with the rotations starting over, you can assume the odds of a Houston win with the series 2-2 would be similar. The obvious retort is that, well, the Nats won two in Houston with Cole and Verlander as the starters. That's certainly true, and Max Scherzer and Stephen Strasburg are almost as imposing, but the reasonable expectation is that they won't pull that off again. No, the Astros at 2-2 would obviously not be as heavy favorites as the Nationals would be at 3-1, but they would be favorites. 

In those ways, Game 4 could be the fulcrum of the 2019 World Series. Win Game 4, and you probably wind up hoisting the trophy. 

Calm down, I said "probably."