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PITTSBURGH -- Pittsburgh closer Joel Hanrahan made sure the Pirates got to celebrate a win after the fireworks went off prematurely at PNC Park.

Hanrahan picked up his 22nd save in as many chances on Saturday in Pittsburgh's 6-4 win over Boston, striking out Adrian Gonzalez to end the game moments after the firework operator got a little giddy on Dustin Pedroia's drive to the wall in rightfield.

The operator, apparently thinking right fielder Xavier Paul had come up with the game-ending grab, started the postgame show. However, Paul couldn't complete the catch and Pedroia raced to second as the fireworks exploded, bringing Gonzalez to the plate representing the tying run.

No biggie. Hanrahan did what he's done all season for the surprising Pirates, shutting the door on the game's top hitter to lift Pittsburgh to its fourth straight win and ruin Tim Wakefield's homecoming.

"You've just got to keep pounding them," Hanrahan said.

He did it for a second straight night as the Pirates sent the largest crowd in PNC Park history home happy by handing the suddenly struggling Red Sox their fourth straight loss.

Lyle Overbay hit a 3-run homer and Jeff Karstens (5-4) pitched effectively into the seventh inning as the Pirates moved two games above .500 at 39-37.

"It's a great feeling out there right now," said Pittsburgh manager Clint Hurdle.

Gonzalez, Josh Reddick and Jacoby Ellsbury all hit solo home runs for the Red Sox, but Boston failed to make Wakefield (4-3) a winner in his first game in Pittsburgh in 18 years.

The 44-year-old knuckleballer gave up five runs on seven hits in six innings, walking four and striking out two. Pittsburgh did most of its damage in the fourth, scoring four runs to erase a 2-0 deficit. Overbay's sixth homer of the season gave the Pirates the lead and Karstens later added the first RBI of his career.

"I felt great except for the fourth," Wakefield said. "It ends up costing us the ballgame."

Wakefield -- the oldest active player in the majors -- was moved up a day in the rotation so the Red Sox could let ace Josh Beckett recuperate from a flu that left him bedridden earlier in the week.

The converted first baseman was a sensation in Pittsburgh nearly 20 years ago, finishing third in Rookie of the Year voting in 1992 after his signature pitch helped lead the Pirates to within a game of the World Series. He posted a pair of complete-game victories in the National League Championship Series against the Atlanta Braves that fall.

Wakefield's win in Game 6 of that series remains the last postseason triumph for the Pirates, a franchise that hasn't finished above .500 since while Wakefield has gone on to win two World Series during his 17 seasons in Boston.

It's a streak of futility the Pirates are desperate to end, and they took another step on Saturday by taking one trip through the lineup before figuring how to handle Wakefield's tricky knuckler.

"It's almost like slow-pitch softball," Hurdle said. "It's a real relaxed mentality, let him deliver the ball and then try to hit it where you think it's going to end up. ... I do think that our guys got some pitches that didn't have as much late movement as it did earlier and were able to square some things up."

The lead grew to 5-2 when Pedroia let a grounder go through his legs in the fifth, though Boston drew back within a run in the seventh behind solo homers by Reddick and Ellsbury.

The Pirates responded with a home run by Garrett Jones in the bottom of the inning and Pittsburgh's bullpen made it stand up. The Pirates are 35-0 when leading after eight innings this season.

"We looked like we were going to come back, and we just couldn't do it," said Boston manager Terry Francona. "Their bullpen just shut us down."

Boston's nine-game interleague road trip -- which includes a visit to Philadelphia starting Tuesday -- is off to a bumpy start, though it's hard to blame Gonzalez.

The first baseman continued his torrid hitting against National League pitching. He began the night batting .543 in interleague play, a number that took a bit of a dip even though he hit his 16th home run of the season and pushed his major league-leading RBI total to 71.

Karstens, thrust into a starting role when Ross Ohlendorf went down with a right shoulder injury, has arguably become the team's most durable starter. He pitched into the seventh inning in each of his past five starts and grinded through a season-high 109 pitches against baseball's top offense, giving up four runs, three earned, on six hits while striking out two.

Though he struggled a bit with his command -- the three walks he issued were one more than he had allowed all month -- Karstens managed to avoid the big inning that has fueled Boston's meteoric rise through the standings the past two months.

"We scored just enough runs to get the W and that's what it's all about," Karstens said.

It helped that he didn't have to worry about facing Boston designated hitter David Ortiz, forced out of the lineup by the National League venue.

Ortiz eventually made his way to the plate as a pinch hitter in the ninth, but grounded out to first following a nine-pitch battle with Hanrahan.

Francona has toyed with the idea of putting Ortiz at first and moving Gonzalez to right field, but stressed before the game he wouldn't do it until he's sure.

The way his offense is sputtering at the moment, he may reconsider. The Red Sox have scored a pedestrian 10 runs during their slide, a number they've matched in a single game nine times this year.

"We can win four just like we lost four, so we're not going to get too up or too down," Pedroia said. "We started the season 2-10 and we've been kicking (butt) ever since, so I don't think anybody's going to go home and jump out of their hotel room because we lost four in a row."

Game notes

Pedroia went 2 for 4 to extend his hitting streak to 10 games. ... Wakefield has started on the road against all but three teams in the majors: Arizona, Washington and the Red Sox. ... The Pirates called up catcher Eric Fryer from Triple-A Indianapolis on Saturday. When he plays he'll become the seventh catcher used by the team this year, the most they've used in one season since 1953. ... Pittsburgh improved to 14-9 in June, assuring the Pirates of their first winning month since June 2009.