(Reuters) - The revitalized St Louis Cardinals made full use of their bullpen to stave off a San Francisco Giants fightback for a 6-4 road victory in the opening game of the National League Championship Series on Sunday.

The defending World Series champions had rallied from a 6-0 deficit in a Game Five decider against Washington on Friday but this time, their own six-run lead was threatened before they held on to draw first blood in the best-of-seven series.

St Louis called on six relievers, who combined for 5 1/3 scoreless innings to finish off a game that had looked to be slipping away when starter Lance Lynn allowed four runs in the bottom of the fourth.

Earlier, David Freese blasted a two-run homer in the second and Carlos Beltran added a two-run shot in the top of the fourth before the Giants, much to the delight of San Francisco's boisterous AT&T Park crowd, mounted their comeback attempt.

The Giants strung together four consecutive two-out hits in their scoring inning, including Gregor Blanco's two-run triple, to rally within two runs but they were unable to make further inroads against the stingy St Louis relievers.

Game Two is in San Francisco on Monday.