He singled in the first inning, then singled again to drive in the final run in the three-run seventh when St. Louis capitalized on fielding blunders by Boston to erase a 2-1 deficit.
"I wanted to be in the lineup. I worked so hard to get to this point," Beltran said. "Somebody would have to kill me in order for me to get out of the lineup.''
And he was on the field when Trevor Rosenthal struck out pinch-hitter Daniel Nava to end the game. Beltran trotted toward center fielder John Jay and left fielder Matt Holliday. They slapped hands and congratulated each other.
The Series resumes in St. Louis on Saturday after a day off with Joe Kelly pitching for St. Louis against Jake Peavy.
Beltran, the club's right fielder, left Wednesday's game after banging into the right-field wall at Fenway as he robbed Red Sox designated hitter David Ortiz of a grand slam in the second inning. He suffered a right rib contusion on the play and was taken to a local hospital, where X-rays and a CT scan were both negative.
"He's a little down right now,'' Cardinals general manager John Mozeliak said after the Cardinals' 8-1 loss Wednesday night. "Obviously he wanted to play in this. To have to come out of the game before it ended was disappointing to him.''
As he did in the series opener, Beltran batted second Thursday night.
Among players with more than 100 career postseason at-bats, Beltran entered Thursday ranked third behind Babe Ruth and Lou Gehrig with a 1.167 OPS. He appeared in 2,064 regular-season games before making his first World Series appearance Wednesday. Among active players, only Miguel Tejada (2,171 games) and Torii Hunter (2,091) had gone longer without playing in a World Series.
Shortly before the Cardinals took batting practice Thursday, Matheny said Beltran planned to test his rib injury in an indoor batting cage. Matheny said that once Beltran received medical clearance, his pain tolerance and ability to play to his usual level would dictate whether he could return to the Cardinals' lineup.
Information from The Associated Press contributed to this report.