Unbeaten in their first Major League Baseball playoff appearance since 1985, the Kansas City Royals advanced to the World Series by defeating the Baltimore Orioles 2-1 on Wednesday.
Meanwhile, San Francisco rallied from a three-run deficit to defeat the St Louis Cardinals 6-4 and move to the brink of winning their playoff series.
The Giants seized a 3-1 lead in the best-of-seven National League final and could advance with a victory in game five on Thursday at San Francisco.
The winner will face the Royals in the World Series championship showdown starting on Tuesday.
The Royals, who won their only World Series title 29 years ago, became the first MLB team to win their first eight playoff games in a season by finishing off a four-game sweep of the Orioles in the best-of-seven American League final.
"It has been awesome," Royals slugger Eric Hosmer said.
"But we're not done yet."
Kansas City will play host to the National League winner, either the St Louis Cardinals or San Francisco Giants, in game one of the best-of-seven championship final next Tuesday.
"We're going to try to make this season even more special," said Royals outfielder Alex Gordon.
"It has been an amazing run. We're playing pretty good baseball."
Should the Royals win their World Series opener, they would equal the all-time longest major league playoff multi-year win streak - 12 games set by the New York Yankees between 1927-1932 and matched by them in 1998-1999 - even with a 29-year gap between wins three and four.
The Royals captured the 1985 World Series by winning the final three games to defeat Missouri state rival St Louis in the maximum seven games.
Since then, Kansas City fans had suffered the longest drought of any major league team without a playoff game, but were rewarded for their patience this October when the Royals beat Oakland in the wildcard game, swept the Los Angeles Angels in the best-of-five division series and dispatched an Orioles squad seeking its first World Series berth since winning in 1983.
The Giants, meanwhile, were trailing 4-3 entering the bottom of the sixth inning and tagged Cardinals relief pitcher Marco Gonzales for three runs to seize command.
San Francisco pinch-hitter Juan Perez walked in the sixth and took second on Brandon Crawford's single. Both runners advanced on Matt Duffy's sacrifice bunt and Gregor Blanco chopped a ground ball to St. Louis first baseman Matt Adams that allowed Perez to race home and beat the throw to the plate with the tying run.
Joe Panik followed with a ground out to Adams, who tried in vain for an inning-ending throw out of Blanco at second base but instead could only watch Crawford scamper home from third with the go-ahead run for the Giants.
When Posey followed with a single to left field, Blanco raced home and San Francisco stretched the lead to the final margin.
