BOSTON — With the help of two Red Sox errors, the St. Louis Cardinals scored three runs in the seventh inning Thursday night to come back and beat Boston 4-2 at Fenway Park in Game 2 of the World Series.

Matt Carpenter’s sacrifice fly scored the tying run, then reliever Craig Breslow’s throwing error brought the go-ahead run home.

David Ortiz had given the Red Sox a 2-1 lead with a two-run homer in the sixth inning.

The Series is now tied 1-1.

“I believe this is a momentum sport,” Cardinals Manager Mike Matheny said. “The guys took charge.”

Game 3 will be at 8:07 p.m. Saturday at St. Louis.

“We expected this to be a hard-fought series,” Boston Manager John Farrell said.

John Lackey and Michael Wacha were locked in a pitcher’s duel. After St. Louis got one run in the fourth after a leadoff triple by Matt Holliday, Ortiz clocked a Wacha change-up over the Green Monster for the lead.

But then came the top of the seventh.

Lackey left with runners on first and second with one out.

Breslow relieved and the Cardinals pulled off a double steal, putting runners on second and third. Breslow then walked Daniel Descalso on seven pitches to load the bases.

Carpenter lined out to Jonny Gomes in left field, scoring Pete Kozma. Catcher Jarrod Saltalamacchia could not handle Gomes’ throw; Breslow backed him up.

Jon Jay took off for third and Breslow tried to throw him out, but sailed the ball over third baseman Xander Bogaerts, allowing Jay to score the go-ahead run, and Descalso to reach third base.

“I’m sure Craig would like to have that ball back and hold it,” Farrell said. “Uncharacteristic of the way we’ve taken care of the baseball this year.”

Carlos Beltran followed with an RBI single for a 4-2 lead.

Breslow said he didn’t regret throwing to third but was disappointed in how he threw it. He also wasn’t pleased with his pitching.

“It still comes down to executing pitches. I didn’t do that,” Breslow said.

Runs were hard to get early.

Lackey allowed singles in the first (Beltran) and second (Yadia Molina) but neither runner got to second base. He pitched a 1-2-3 third with two strikeouts.

Wacha, meanwhile, was dealing, retiring eight of the first nine batters (Mike Napoli walked in the second).

Jacoby Ellsbury got Boston’s first hit with a two-out, broken-bat single in the third.

Holliday led off the fourth for St. Louis. In his first at-bat, Lackey threw him all fastballs and struck him out.

In the fourth, Holliday swung and missed at a first-pitch fastball. Lackey came back with another fastball and Holliday drilled it to the triangle in center field. It bounced away from Ellsbury and Holliday easily made it to third base.

Matt Adams lined out to Dustin Pedroia at second base. Holliday stayed put.

Molina then hit a high bouncer. Lackey stretched out his 6-foot-6 frame but couldn’t glove it. Pedroia charged in and snagged it. Pedroia looked home, saw he had no chance at Holliday and threw Molina out.

The groundout RBI gave St. Louis a 1-0 lead. It was the first time the Cardinals led Boston in a World Series game since 1967; the Red Sox never trailed in 2004.

Pedroia led off the Boston fourth with a double off the Monster. Ortiz followed with a walk and the Fenway crowd had something to get excited about.

But Napoli grounded into a double play and Gomes popped out.

Pedroia got another rally going when he walked with one out in the sixth.

Wacha was at 98 pitches but the Cardinals kept him in against Ortiz.

Ortiz worked the count full. Wacha delivered a change-up. Ortiz swatted it out for a 2-1 lead.

“Those guys battled me all night,” Wacha said.

Lackey looked in control and began the seventh inning with his sixth strikeout. He got ahead of David Freese 2-2, but walked him on eight pitches.

Lackey got ahead of Jay 0-and-2, but Jay then singled on a 1-2 pitch, ending Lackey’s night.

Breslow came in and … well, you know by now.

Down 4-2 in the eighth, Boston put two runners on, Ellsbury reaching on an error and Ortiz singling. But reliever Carlos Martinez got Napoli to pop out.

Closer Trevor Rosenthal struck out the side in the ninth.

Kevin Thomas can be reached at 791-6411 or:

kthomas@pressherald.com

Twitter: @ClearTheBases