Giants 6, Reds 4: Buster Posey capped a six-run fifth inning with a grand slam and visiting San Francisco completed a historic comeback to advance to the National League Championship Series.

The Giants became the first NL team to win the Division Series after losing the first two games and the first major-league team to overcome an 0-2 deficit in a five-game postseason series by winning three consecutive games on the road. San Francisco begins the NL Championship Series against either St. Louis or Washington on Sunday.

Posey crushed a 2-2 pitch to left field off Mat Latos (0-1) for the third postseason grand slam in Giants history after Brandon Crawford tripled in a run and scored on an error to break a scoreless tie.

The Reds answered with two runs in the fifth and one in the sixth before Sergio Romo recorded four outs for the save. Romo allowed Ryan Ludwick's RBI single with one out in the ninth before retiring Jay Bruce and Scott Rolen to end the game.

Brandon Phillips had two hits and two RBIs for Cincinnati, which was outscored 16-8 over the last three games after never losing three consecutive home games during the regular season. The Reds left 11 runners on base and were 2-for-13 with runners in scoring position.

Cincinnati had runners at first and second with no outs in the seventh after Ludwick led off the inning his third homer of the series to pull the Reds within 6-3. The Giants escaped the threat when Matt Cain (1-1) struck out Ryan Hanigan and Posey threw out Bruce attempting to steal third before Drew Stubbs grounded out against George Kontos to end the inning.

The Reds threatened again in the eighth with two on and two outs before Angel Pagan made a diving catch on Dioner Navarro’s fly ball to shallow center field.

GAME NOTEBOOK: Posey’s blast was the first career grand slam allowed by Latos, who posted a 2.19 ERA in 11 previous starts against the Giants. … Beginning with Game 6 of the 2002 World Series, Reds manager Dusty Baker’s teams are 1-9 when playing with a chance to clinch a postseason series. …Giants 1B Brandon Belt struck out three times in four at-bats and went 1-for-11 in the series. … NL teams were 0-21 since the Division Series was added in 1995, and overall 38 of the 42 teams that led 2-0 in the Division Series had advanced. ...Cain allowed three runs over 5 2/3 innings.