Alvarez hit a tiebreaking single in the eighth inning and the Pirates beat the St. Louis Cardinals 5-3 on Sunday to take a 2-1 lead in best-of-five NL division series.
Alvarez pulled a grounder into right field that scored pinch-runner Josh Harrison from second base. Russell Martin followed with a sharp RBI single against reliever Kevin Siegrist, who took over after Carlos Martinez (0-1) faltered.
The go-ahead single was the latest big hit by Alvarez. He homered in the first two games of the series and is 4 for 10 with four RBIs.
Alvarez also kept the Pirates' famous flag flying high in October. ''Raise the Jolly Roger!'' is the rallying cry for this wild-card team, now one victory from its first postseason series win since the 1979 World Series.
Beltran finished 2 for 3 with three RBIs. His 16th postseason home run moved him past Babe Ruth for eighth place in postseason history.
Beltran's shot temporarily silenced a rocking crowd at PNC Park. It also set the stage for another dramatic win by the Pirates.
Andrew McCutchen led off the eighth with his second hit, a double to left. But the NL MVP candidate unwisely tried to advance on Justin Morneau's grounder to shortstop and was an easy out at third.
Harrison ran for Morneau and moved up when Marlon Byrd walked. St. Louis manager Mike Matheny turned to the lefty Siegrist to face the left-handed Alvarez. The Pittsburgh slugger tied for the NL lead with 36 homers in the regular season, but hit just .180 against lefties.
Alvarez responded with his single between first and second. Martin then tried to drop down a squeeze bunt to score Byrd from third - he fouled it off, then lined a hit to left that gave Grilli more than enough cushion.
Martin's sacrifice fly off reliever Seth Maness in the sixth gave the Pirates a 3-2 lead and turned the game over to Pittsburgh's ''Shark Tank'' bullpen, one of the keys to the franchise's first winning season and playoff berth in 21 years.
Tony Watson worked around a one-out single in the seventh before giving way to Melancon in the eighth.
Melancon stepped in capably for a while when Grilli, the All-Star closer, went down with a strained right forearm in July. But Melancon struggled down the stretch and his fourth blown save in the last three weeks came courtesy of Beltran, who knows a thing or two about delivering this time of year.
Pirates starter Francisco Liriano dominated the Cardinals during the regular season, going 3-0 with an 0.75 ERA in his three starts against the NL's highest-scoring team. He was electric in Pittsburgh's wild-card win over Cincinnati last Tuesday, shaking off a sinus infection and baffling the Reds with a series of changeups and sliders that ended Cincinnati's season and manager Dusty Baker's tenure.
The sharpness that fueled Liriano's career-reviving year abandoned him after his first trip through the St. Louis lineup. He narrowly escaped the third inning when Matt Holliday lined to right with the bases loaded.
Liriano wasn't quite as fortunate in the fifth. Jon Jay led off with a single and Pete Kozma followed with a walk. After Joe Kelly struck out trying to bunt, a double steal set up Beltran's two-run single.
At 2-all, the Cardinals had matched their entire output against Liriano in their previous 28 innings.
Liriano was matched nearly pitch for pitch by the unflappable Kelly. The 25-year-old right-hander has been rock steady all season, even as he moved from middle reliever to starter in July.
Kelly welcomed the hostile environment, calling the sea of black-clad fans that awaited him one of the things a kid dreams about.
The reality proved a little more unnerving, at least early.
Kelly walked McCutchen with two outs in the first and Morneau followed with a line drive that smacked off the pitcher's leg and rolled weakly behind the mound. Kozma's rushed throw from shortstop skipped into the stands, putting runners in scoring position for Byrd.
The well-traveled outfielder - who played in 1,250 regular- season games before reaching the playoffs for the first time - has been a welcome jolt both in the lineup and in the clubhouse for the Pirates. He delivered again, hitting a two-run single that put the Pirates ahead.
Link to box score: Pittsburgh 5, St. Louis 3
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