Crafting a World Series clean sweep with masterful pitching and clutch hits, the San Francisco Giants won a second Major League Baseball title in three seasons on Sunday with a 4-3 victory over Detroit.

The Giants routed Detroit 4-0 in the best-of-seven final and after a 2010 Series triumph over Texas, this latest victory was the club's seventh championship overall, with five of them coming before the team moved from New York in 1958.

"I'm numb to the fact we've won two World Series in the past three years. I'm kind of speechless," Giants manager Bruce Bochy said.

"It's amazing. I'm proud of a group of guys who were not going to be denied. I couldn't be prouder of a group who played the game so well."

Ryan Theriot, who won a World Series last year with St. Louis, scored the title-winning run for the Giants in the 10th inning on a single by Marco Scutaro, who made the key hit two days before his 37th birthday.

Theriot singled to right field, advancing to second base on Brandon Crawford's sacrifice bunt and raced home on a two-out single by Scutaro, who has played for six different clubs in 10 major league seasons.

Giants relief ace Sergio Romo entered in the bottom half of the 10th and struck out leadoff hitter Austin Jackson, pinch hitter Don Kelly and Tigers slugger Miguel Cabrera for the last outs to ignite a victory celebration.

San Francisco became the 21st team to capture the throne in a sweep and kept the Tigers searching for their first World Series crown since 1984.

"I'm a little bit flabbergasted to be honest," Tigers manager Jim Leyland said. "I would never have thought the Giants would have swept us, but it happened. It's a freaky game. It happened. So be it."

San Francisco third baseman Pablo Sandoval was named Most Valuable Player of the World Series.

The Venezuelan slugger nicknamed "Kung Fu Panda" blasted three home runs in the Giants' game-one triumph and had 24 total hits in the playoffs including six homers, five doubles and 13 runs batted in during the title run.

The Giants were often on the brink of elimination in the playoffs, winning the last three games of their first post-season series against Cincinnati then needing to take the last three against St. Louis to reach the World Series.

With San Francisco trailing for the first time in the World Series, Buster Posey blasted an off-speed offering from Detroit pitcher Max Scherzer into the left-field stands for a two-run homer that gave the Giants a 3-2 lead in the sixth inning.

Scutaro had led off the sixth with an infield single down the third base line and Posey made it pay off with his blast just inside the foul pole to put Detroit behind once more.

But Delmon Young answered for the Tigers in the home half of the sixth by smashing the first pitch he saw from Cain into the right-field stands for a solo homer to equalise at 3-3.

Cabrera, the star slugger who only had been hitting 2-for-9 in the World Series, had smacked a two-run homer in the third inning to give the Tigers a 2-1 advantage and end a run of 20 scoreless innings for Detroit.

San Francisco took a 1-0 lead in the second inning when Hunter Pence bounced the ball over the centre-field wall for a ground rule double and scored when Brandon Belt, who had been 0-for-10 in the Series, tripled to right field.