PITTSBURGH -- The Pittsburgh Pirates have struggled so mightily to score runs this season, they weren't going to let one practically handed to them get away.
Neil Walker advanced to third when New York center fielder Kirk Nieuwenhuis misplayed Walker's deep fly ball leading off the eighth and Walker scored on Clint Barmes' sacrifice fly two batters later to lift the Pirates to an unlikely 5-4 victory.
"It's a gift and we were able to cash it in," Pittsburgh manager Clint Hurdle said.
Walker's fly ball off reliever Jon Rauch (3-3) appeared to be harmless when it left the bat. Nieuwenhuis and left fielder Mike Baxter - both of whom entered the game as pinch hitters in the top of the eighth - moved toward each other to play it, with Nieuwenhuis raising his arm to call off Baxter.
Problem is, Baxter never stopped coming. The two were standing next to each other when the ball caromed off Nieuwenhuis' mitt and rolled to the wall.
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"You're out there and there's a lot of noise, Mike is calling for it, Kirk is calling for it and they can't hear each other," New York manager Terry Collins said. "But once the center fielder calls it, it's his ball. Somehow Mike has to know the center fielder is coming. We've just got to catch the ball there."
Walker raced to third then gave the Pirates their first lead when he slid just under the tag of catcher Mike Nickeas following a wide throw from Lucas Duda.
"We had to send him," Hurdle said of Walker. "There was no not sending him."
Mike McKenry tied it with a two-run homer in the seventh off starter Johan Santana, who couldn't protect an early 4-0 lead.
Jared Hughes (1-0) earned his first major league win in relief. Joel Hanrahan worked the ninth for his 10th save.
David Wright had two hits for the Mets to lift his batting average to a major league-best .415. Ex-Pirate Ronny Cedeno added two hits, but New York committed three errors and lost for the fifth time in seven games.
Santana has shown flashes this season of the form that made him a two-time AL Cy Young Award winner, though it has rarely translated into victories. He has six no-decisions after letting one of baseball's worst offenses chip away at his early cushion.
The Mets, who have struggled scoring runs when Santana is on the mound, staked him to a 4-0 lead in the second when Pirates starter Erik Bedard temporarily lost the command that has given the top of Pittsburgh's rotation a steady presence this season.
Vinny Rottino, called up from the minors earlier in the day, singled with one out and Cedeno - a former Pittsburgh shortstop who signed with the Mets in the offseason and was booed constantly - doubled to right-center to give New York the lead.
Two walks sandwiched around a sacrifice bunt loaded the bases and Justin Turner delivered a two-run single. Wright followed with a RBI single and the Mets appeared in business against the Pirates, who entered the game 6-20 when allowing an opponent to score at least four runs.
Pittsburgh chipped away in the fourth thanks to three consecutive doubles by Josh Harrison, Andrew McCutchen and Pedro Alvarez - who recorded just the fifth hit by a left-handed batter off Santana this season.
Santana escaped the fourth when McKenry hit into a double play, though the backup catcher atoned in the seventh, taking an 87 mph fastball and drilling it into the seats in left to tie the game.
"You just take whatever you can get from a guy like that," McKenry said. "Luckily he left a pitch up for me."
Santana gave up four runs and eight hits in 6 1-3 innings, walking two and striking out seven as his ERA rose from 2.89 to 3.24.
"The pitch to McKenry is a ball I'm sure he'd like to get back," Collins said of Santana. "It was a pitch up. But the big difference is we didn't add on. When they scored two runs (in the fourth), we had several opportunities to get them back and we didn't."
Instead, the Mets then did their best to give it away and for once the Pirates took advantage. Pittsburgh is near the bottom of the National League in every major offensive category but somehow remains hovering around .500 (20-22) thanks to a solid pitching staff and a fair amount of grit.
Both were on display late.
"Good things happen when you stay in games," Barmes said. "We found ways to get some quality at-bats against a quality pitcher. It was definitely a big win for us tonight."
Mets C Josh Thole, on the seven-day disabled list with a concussion, has been cleared to begin baseball activities but there is no timetable for his return. ... Pittsburgh starting pitcher Jeff Karstens worked three scoreless innings in a rehab start at Double-A Altoona. Karstens gave up two hits and had one strikeout. Karstens has been on the disabled list since April 17 with right shoulder inflammation. ... The series continues Tuesday, with New York knuckleballer R.A. Dickey (5-1, 3.75 ERA) facing Pittsburgh's James McDonald (3-2, 2.68).