Peter Bourjos sailed a throw to the plate from center with the lead baserunner holding at third, but Martinez failed to get behind catcher Yadier Molina. The throw ricocheted off his glove to the backstop, allowing the runner to score. From there, the Giants added two more runs on the Cardinals' bullpen before closing out a 6-5 series-opening victory at Busch Stadium.
"As soon as that ball is hit, they all know they have to be behind the catcher," manager Mike Matheny said. "He was in the wrong spot and it ended up hurting."
Allen Craig, who has spent much of the early part of the season searching for consistency out of his bat, continued to prove he's found it when he hit a go-ahead solo homer to right-center to give the Cardinals a lead in the sixth.
The Giants had other plans. Martinez, who relieved starter Jaime Garcia after seven innings, allowed a leadoff single. After a popout, center fielder Angel Pagan stepped to the plate with left fielder Gregor Blanco at first. Pagan's single back through the middle sent Blanco to third, where he was held.
At least until Bourjos fired his throw, which bounced short of home plate as Martinez, standing in front of Molina, attempted to field it before jumping out of the way, the ball shooting past Molina to score the game-tying run. After Pagan advanced to third on a groundout and Martinez intenionally walked Pablo Sandoval, Trevor Rosenthal allowed a two-run double to first baseman Michael Morse to give the Giants, the Majors' best team, the lead on the second pitch he threw in relief of Martinez.
"That was a good break for us," Giants manager Bruce Bochy said. "[Third-base coach Tim Flannery] was holding [Blanco] up, which was the right thing. He's a good outfielder with a good arm and he was right on top of us."
"He's an athlete that wants to be on top of every play," Matheny added. "That's not the right play."
The mistake erased a win for Garcia, who lasted seven innings while allowing three runs.
Garcia surrendered two runs to the Giants in the second. The first came when he left a slider over the plate to Morse, who hit it 442 feet over the left-center-field wall. Two singles brought another runner around.
Garcia settled down from there, allowing only two other baserunners. One came on his one other mistake, a 2-1 changeup left over the plate to Sandoval, who hit it over the wall to tie the game in the sixth.
"You go out there, try to get ahead and try to keep the ball down," Garcia said. "Unfortunately today I made some mistakes and I feel like I didn't do my job. We lost the ballgame."
Craig picked his starter up in the bottom half of the sixth, taking the third pitch of the inning -- an 87 mph slider -- over the wall for his sixth homer of the season to recapture the lead and put Garcia in line for his second win in three starts.
Craig drove in the Cardinals' first run after Matt Carpenter extended his hitting streak to 11 games and stole second. The first-inning double from Craig gave him hits in eight of the last nine games.
"I felt like I had a good approach tonight and I was aggressive," Craig said. "I did a good job of swinging at the balls that were in the zone and hit the ball decent."
The Cardinals also missed opportunities to score. They settled for two runs in the fourth after loading the bases with no outs. A double play brought in the first run and a single the second but Jon Jay was thrown out trying to extend to second.
They also failed to score in the fifth after Bourjos went from first to third on a sacrifice bunt with one out, eventually stranding runners on second and third.
"When you don't get the runs out of it, that's what hurts," Matheny said. "Usually those turn into runs, but unfortunately we weren't able to get the job done."
Carpenter pulled the Cardinals to within a run with a two-out RBI single in the ninth before Giants closer Sergio Romo finished off his 17th save. The Cardinals ended the game with runners on the corners when pinch-hitter Shane Robinson popped out to third.
The game, ultimately, swung with one play in the eighth that had nothing to do with Martinez's stuff.
"We definitely had a bead on that game," Craig said. "It felt like we were going to win it, but that's baseball. We just didn't make enough plays."