ST. LOUIS -- In manager John Russell's plan, outfielder Jason Bay was never going to swing a bat in Thursday's game against the Cardinals.

That's why Bay didn't come off the bench to pinch-hit in the fifth with two on against Joel Pineiro, a pitcher he had gone 4-for-8 against in his career.

But when an eighth-inning situation dictated another Pittsburgh pinch-hitter, Bay got the call.

He saw four pitches against Cardinals reliever Jason Isringhausen, lifting the fourth one -- a low fastball -- just over the left-field wall and into the Pirates' bullpen for a game-winning, three-run homer.

"It was unexpected, but a very good day nonetheless," said Bay, who now has eight homers this season. "Couldn't have picked a better off-day I guess."

The final 11-5 score at Busch Stadium masked the fact that up until the eighth, the Pirates offense never looked as if it would run away with the rubber game of the three-game set.

On an overcast day when a steady rain made a three-hour, 32-minute game seem much longer, the Pirates scored 10 unanswered runs after falling into an early 5-1 hole.

A game that was sealed by Bay's home run was led by a supporting cast of Doug Mientkiewicz, Ronny Paulino and Chris Gomez -- the lineup's sixth through eighth hitters -- who combined to go 8-for-13 with two walks and eight runs scored. Fittingly, it was those bottom three hitters who set the stage for Bay's blast.

After connecting for just six hits in his previous 41 at-bats, Mientkiewicz reached base all five times he stepped to the plate on Thursday. With the Pirates trailing 5-4, the utility infielder began what would be a four-run eighth with a walk off Isringhausen -- who had been taken out of the closer's role last weekend -- before Paulino singled.

Gomez then laid down a sacrifice bunt that Isringhausen fielded. He had a play at third to get the lead runner, but he threw the ball into left field, and Mientkiewicz trotted home with the tying run.

That brought up Bay, who had been taking swings down the tunnel during the previous few innings with the feeling that he may be called on late.

"Every day I don't get in, I fully anticipate getting in at some point, so I'm kind of ready," said Bay, who came into the game 1-for-11 as a pinch-hitter.

His intention was to get the ball in the air to drive home a run on a sacrifice fly. He'd do two runs better.

"It was so high, and it just started drifting," Russell said. "I really didn't think that one would [get out]. It just kept carrying."

It carried just enough to give the Pirates an 8-5 lead.

"When you get a day off and you do something like that, it's even more special," Russell added.

The Pirates tacked on three more runs in the ninth -- again with the bottom of the order leading the way -- to seal the team's first three-game series win at Busch Stadium since May 2003. The victory also inched the Pirates back to within one game of .500.

The feisty, late-inning, come-from-behind win had been made necessary by another frustrating outing for Ian Snell.

"I'm just trying to find my way," said Snell, who allowed 11 hits and five runs over a season-short four innings. "I don't understand it. I'm trying to understand [the struggles], I just can't."

Though the team's comeback would ensure that he wouldn't drop his third straight decision, Snell is still winless since April 12.

"I'm trying everything possible," he continued. "I don't know what has happened this year compared to last year. I am the one who got us into that mess."

But by the end of Snell's disappointing outing, maybe his most important number of the dreary afternoon was eight -- the number of St. Louis runners that he stranded. Doing so kept the game within reach.

That included getting Albert Pujols, who came into the game 11-for-19 against Snell, to ground out with two on in the second. It also took a diving catch from Nate McLouth with the bases loaded in the first to preserve was what at the time a 1-1 game. McLouth had gotten the Pirates on the board early with a solo homer in the first.

The Pirates were able to finally carve into a 5-1 deficit in the fifth. Back-to-back-to-back singles by Mientkiewicz, Paulino and Gomez pushed one across for the Pirates. Jason Michaels, Bay's fill-in in left field laced a two-out, two-run single to right.

Like the bottom of the order, the Pirates' bullpen would also come up huge in solidifying the win. Five relievers combined to toss five scoreless innings, highlighted by John Grabow coming in and stranding two St. Louis runners in the seventh with the Pirates trailing by one.

"Grabow coming in and shutting the door with men on base was really special for us," Russell said. "We know we're in the game until it's over. If the pitching gives us the opportunity to score, late in the game we do a pretty good job of that."