Alvarez hit a grand slam in the first inning off suddenly scuffling 10-game winner Lance Lynn and Andrew McCutchen had two hits before leaving with a sprained left wrist as the Pirates beat the St. Louis Cardinals 7-3 Saturday for their fourth victory in a row.
''I'm the guy who kept running him out there. Not everybody was on that bandwagon,'' manager Clint Hurdle said. ''There weren't a lot of `Pedro for Mayor' signs being hung up in the ballpark.
''We know this guy's significant in a lot of different ways and we had to ride this out and see where it took us,'' he said.
The Pirates got good news on a player they can't afford to lose, too. X-rays showed no significant injury to McCutchen, who tweaked his wrist making a diving catch.
''I thought it was awesome and then I thought he was hurt,'' pitcher Jeff Karstens said. ''And I was like, `I wish he'd have missed it and not dived.
''He's our best player, there's no ifs and buts about it. He's electric, he changes the game.'
Manager Clint Hurdle said McCutchen will probably rest on Sunday.
''I don't get days off, I'm not trying to get days off,'' McCutchen said. ''I get days off in the offseason.''
Jeff Karstens (1-2) thrived in sweltering heat, allowing four hits with seven strikeouts in seven strong innings for his first victory since Aug. 10, 2011 at San Francisco. Karstens changed his pregame routine, running and stretching inside, and then confounded the Cardinals by changing speeds.
Pittsburgh matched its longest winning streak of the year aided by fast starts with 11 first-inning runs the last three games, and stayed one game back of NL Central-leading Cincinnati. It was 99 degrees for the first pitch and the temperature spiked to 103 later in the game.
The Pirates are a season-best seven games above .500 after finishing June 17-10, their most victories in a month since August of 2007. If they complete their first three-game sweep in St. Louis since May 27-29, 1991 on Sunday it'll mark the franchise's high water mark since the final game of their 96-66 NL East championship team in 1992. Erik Bedard (4-8, 4.27 ERA) opposes Jake Westbrook (6-6, 3.77).
''We have a very good team,'' Alvarez said. ''We've just got to keep it going and not change anything.''
Carlos Beltran drove in a run with his 400th career double off Tony Watson in the eighth for St. Louis, one night after getting his 2,000th career hit. Beltran has an eight-game RBI streak, longest in the majors this season, and leads the league with 61 RBIs.
Jared Hughes retired the last four batters in order for his first career save as the Cardinals fell to 17-18 at home.
McCutchen, who leads the Pirates with a .346 average and 51 RBIs with 15 homers, was removed for a pinch hitter in the seventh, four innings after sprawling to catch Beltran's sinking liner. McCutchen also banged into the center field wall in an unsuccessful bid to rob Tony Cruz of a double to start that inning.
''I missed it, man,'' McCutchen said. ''That would have been a sick catch if I caught it.''
Alvarez is 2 for 2 with an astounding 10 RBIs with the bases loaded, the other hit a three-run double to go with two sacrifice flies and a walk. He has 13 RBIs in five games in St. Louis and 15 total against the Cardinals, most of any opponent.
The 25-year-old Alvarez, the second overall draft pick in 2008, batted just .191 in an injury-shortened 2011 and was hitting just .205 after the first two months this year. Though he's still batting just .226, in June he emerged with seven homers and 20 RBIs.
''I like getting an opportunity to play, no matter where it's at,'' Alvarez said. ''That kind of production, it's just a coincidence. I never know one of these things until someone brings it up.''
Lynn (10-4) was pummeled for the third straight start, surrendering six runs in five innings. Since combining for 23 strikeouts in consecutive victories earlier this month, the first-year starter who replaced injured Chris Carpenter in the rotation has given up 17 runs on 25 hits in 15 1-3 innings.
The 25-year-old right-hander said his troubles have nothing to do with fatigue.
''This is the best I've felt all year, and I'm not getting the job done,'' Lynn said. ''You have times when you feel good and things don't go your way and then some when you feel bad and thing's seem to go your way.
''It's part of the game and that's just the way it is.''
The Pirates homered an NL-leading 39 times in June to tie the franchise record set in 1975, and lead the league with 51 road homers.
Lynn got a pair of groundouts to open the game before running into trouble. McCutchen and Garrett Jones singled to put runners at the corners and Neil Walker walked before Alvarez swatted a full-count fastball into the right-field stands for his second career grand slam and 15th homer overall, tying McCutchen for the team lead.
''You can't give that guy a chance to do anything in the first inning, and I just didn't get it done,'' Lynn said. ''It cost us the whole game right off the bat.''
Karstens totaled 17 innings in his first four starts of a season interrupted by a shoulder injury. He struggled only in the third when Cruz scored on Jon Jay's groundout and Matt Holliday added an RBI single to cut the deficit to 4-2.
NOTES: The Pirates have won 11 of their last 14 against the NL Central. ... Holliday had two singles and a walk and is batting .500 (25 for 50) the last 12 games with two homers, eight doubles and 13 RBIs. ... The grand slam by Alvarez was the Pirates' first since Derrek Lee against the Cubs' Carlos Marmol last Sept. 3. ... Cardinals 3B coach Jose Oquendo missed his second straight game because of illness. ... Cardinals LHP Barret Browning, whose contract was purchased earlier in the day from Triple-A Memphis, worked two perfect innings in his major league debut after replacing Lynn.
Link to boxscore: Pittsburgh 7 at St. Louis 3