Manager Brad Mills is still confident that Martinez's power will continue to develop this season. The outfielder, who went deep on Sunday against the White Sox in Chicago, leads the Astros with 33 RBIs heading into Wednesday's game against the Giants at AT&T Park.
"He's got a lot of power," Mills said. "The situation with J.D. is he just has the ability to put a quality at-bat together with runners in scoring position. That's kind of nice to have. You want everybody to be that way, but he does a good job of doing that, having solid at-bats and putting them together."
Martinez and the Astros will face Giants right-hander Matt Cain, who has given up only three homers in his last 55 2/3 innings and will be looking to win his seventh straight start.
Cain, whose Giants beat the Astros, 6-3, in the series opener on Tuesday, has a 0.83 ERA in his last 21 2/3 innings, a span of three outings. He has won each of his last six starts since May 12.
In his last trip to the hill, Cain went seven innings against the Padres, striking out nine and not giving up any earned runs in an 8-3 victory.
"I felt like I stayed in a rhythm and at times tried to slow the game down to where I didn't get out of whack," Cain said after the start.
Cain (7-2) has gone at least six innings in all 12 of his starts in 2012. That's the longest streak by a Giants pitcher to open a season since Atlee Hammaker started the 1983 season with 21 starts of six or more innings.
As Cain looks to keep his winning streak going, the Astros' J.A. Happ is trying to avoid his fourth consecutive loss.
Happ (4-6) hasn't been bad in his last three starts, giving up nine runs in 18 innings of work, but the run support just hasn't been there. The Astros have scored four total runs in Happ's last three outings.
In his last start, Happ gave up four runs and five hits in 4 2/3 innings against the Cardinals.
Giants: Posey leading NL catcher vote
Catcher Buster Posey tops all National League catchers in voting for the All-Star Game in Kansas City on July 10. Posey has 1,713,839 votes and leads the Cardinals' Yadier Molina by 137,640 votes.
Four other Giants cracked the All-Star voting update, released on Tuesday. Pablo Sandoval is second among NL third basemen, Melky Cabrera is fourth among NL outfielders, Brandon Belt is fourth among NL first basemen and Angel Pagan is 12th among NL outfielders.
Cain is holding right-handed batters to a .176 average and left-handers to a .247 average. Right-handers have accounted for five of the seven homers hit off Cain this season.
Astros: Bixler gets first RBI for Astros
With a single in the third inning, Brian Bixler drove in his first run for the Astros.
It was Bixler's first Major League RBI since August 11, 2011, for the Nationals. Bixler was recalled from Triple-A Oklahoma City on June 8.
Bixler also picked up an RBI with a double in the eighth.
The Astros are 0-6 in extra-inning games this season.
Cain hasn't been especially dominant in his career against the Astros, posting a 1-3 record with a 4.69 ERA in seven games (six starts) against Houston. He last beat the Astros on May 13, 2008.