Werth, named Friday as an All-Star replacement for injured New York Mets outfielder Carlos Beltran, gave the Phillies a 3-1 lead with his extra base hit.
Blanton (6-4) allowed four hits and a run over 7 1/3 innings to win his second straight start. The back-to-back victories have come following a five-game winless streak.
Romero recorded the final two outs of the eighth inning and the first in the ninth before Lidge came on to pick up his 18th save. Lidge allowed a two-out homer to Brandon Moss and then gave up a single to Jack Wilson, but got Delwyn Young on strikes to end the game.
Zach Duke (8-8) was the hard-luck loser, giving up the three runs on five hits over eight innings. He has lost his last three starts.