Pedro Alvarez hit a go-ahead, two-run double to start a seven-run fifth and matched his career high for RBIs in a season with 85. Russell Martin and Gaby Sanchez added sacrifice flies and Tabata had a three-run double in his second plate appearance of the inning.
Giants right-hander Matt Cain departed after getting hit on his pitching arm on a line drive by Sanchez. X-rays on Cain's bruised forearm were negative.
Jones' 12th homer leading off the second was a splash-hit drive into McCovey Cove beyond the right-field wall. It was the 28th at AT&T Park by an opponent and second by a Pirates player. Adam LaRoche hit one on Aug. 11, 2007, against Tim Lincecum.
Cain was hit when Sanchez led off the fourth with a groundout. Trainer Dave Groeschner and manager Bruce Bochy hustled out to check on the pitcher, who walked off the mound on his own moments later.
He allowed three runs and seven hits in 3 1-3 innings. Guillermo Moscoso (1-2) relieved with the Giants trailing 3-1.
Cain, who had been on a nice roll since the All-Star break, threw 64 pitches, 40 for strikes.
Tabata added a pair of singles for his third three-hit game in August.
On a day the Giants lost outfielder Andres Torres perhaps for the season to a strained left Achilles tendon, the defending World Series champs were dealt another blow with the early exit for Cain. San Francisco was outscored 21-4 in a losing three-game series against the Red Sox -- including 12-1 in Wednesday's finale.
It wasn't much better in the opener of a four-game series with the Pirates. Brandon Crawford added a two-run double in the eighth for San Francisco.
Third baseman Pablo Sandoval returned to the Giants' lineup after missing two games with a sore back. He grounded into a double play in the second and wound up 1 for 3 with a walk.
NOTES: Pirates GM Neal Huntington said LHP Wandy Rodriguez (forearm tightness) felt pain during his simulated game and will be examined by Dr. James Andrews early next week. ... Giants manager Bruce Bochy said struggling LHP Barry Zito (4-9, 5.63 ERA) is scheduled to make his next start. "We're keeping the guys in the rotation where they're at," Bochy said. ... Pirates RH closer Jason Grilli, nursing a strained tendon in his throwing arm, threw a 25-pitch bullpen and is scheduled for another side session Sunday before a likely rehab outing. "Another good day day for Jason," manager Clint Hurdle said. "We'll see how he bounces back tomorrow." ... Hurdle believes OF Starling Marte is close to returning and won't need a DL stint. He missed his fourth straight game because of a bruise on his right hand after getting stepped on during a headfirst slide against Arizona on Sunday. "I think Marte is right on the edge of coming back," Hurdle said. "He's closing in on that -- return to play." ... The Giants are 9-22 vs. the NL Central.