(Reuters) - The San Francisco Giants routed the St. Louis Cardinals 9-0 in Game Seven of the National League Championship Series on Monday to complete a stunning comeback and advance to the World Series against the Detroit Tigers.

The Giants, the 2010 World Series winners, trailed last year's champion Cardinals 3-1 in the best-of-seven series but ran off three straight victories by a combined score of 20-1 to win the National League championship four games to three.

San Francisco will host the American League winning Tigers, who swept the New York Yankees 4-0 to win the pennant, in the first two games of Major League Baseball's championship starting with the opener of the Fall Classic on Wednesday.

A five-run burst in the third inning blew the game open for the Giants, who had scored single runs in the first two innings for a 2-0 lead.

The key blow was a fortuitous, spinning double off the broken bat of Hunter Pence with the bases loaded and no outs that scored three runs. Some shaky fielding by the Cardinals allowed the Giants to add two more runs to run off to a 7-0 lead.

The victory for the Giants was their sixth do-or-die triumph of this postseason, after fighting back to win the last three games on the road in their best-of-five Division Series with the Cincinnati Reds.

Matt Cain was the winning pitcher in the decider, throwing five and two-thirds innings of shutout ball, allowing five hits and one walk with four strikeouts. St Louis starter Kyle Lohse gave up six hits and five runs in two-plus innings.

(Reporting by Larry Fine in New York, Editing by Julian Linden)