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CHICAGO -- Jeff Samardzija knows his role with the Chicago Cubs may soon become much more prominent.

He looked up to the task Wednesday night, battling without his best stuff as the Cubs beat the Miami Marlins 5-1 in a rain-shortened game.

Starlin Castro homered for Chicago and the Cubs batted around in a four-run seventh.

Heavy rain began falling with Miami batting in the top of the eighth and the teams never returned to the field. The game was called after a 1-hour, 17-minute delay.

Samardzija was effective for a third consecutive outing, allowing one run over five innings, though he did not factor in the decision.

He got out of a jam in the fifth despite Emilio Bonifacio's leadoff triple. Logan Morrison hit a grounder with the infield in, but catcher Geovany Soto bobbled the throw on a botched rundown to put runners at second and third. Samardzija struck out Ramirez and got Greg Dobbs to ground out to end the threat.

Samardzija was lifted for a pinch hitter in the fifth. He finished with nine strikeouts and two walks, scattering six hits.

"After that rundown, I kind of just took a second. That's what I was happy about, just taking my time and not rushing, making the pitches I needed to make," Samardzija said. "Things like that, you learn from it. You never know when that situation will come up again, but at least you can go back on when it happened before and rely on your past experience."

With teammates Ryan Dempster and Matt Garza being mentioned in trade rumors, Samardzija may soon vault into the No. 1 spot in the Cubs rotation.

"I understand what my role is on this team and what it's going to be in the future," he said. "I'm really trying to do everything I can today so down the road when you are relied upon, you're ready to take the reins and do what you got to do."

After a rough June, Samardzija has given up just five runs in 19 innings this month.

"He wasn't as efficient. First-pitch strikes were tough for him all night," Cubs manager Dale Sveum said of Samardzija. "That's the kind of guy he is, he made all the pitches he had to, and that's what good pitchers do. When they have to do it, they get it done."

Castro hit his eighth home run of the season off Marlins starter Josh Johnson (5-7) leading off the fourth. Jeff Baker highlighted the seventh-inning rally with a two-run, pinch-hit double with the bases loaded.

James Russell (3-0) pitched a scoreless seventh to earn the victory.

Jose Reyes ripped an 0-2 delivery over the wall in right field leading off the third to put the Marlins up 1-0. It was his fourth homer of the year, but it was all the offense Miami could muster.

The Marlins left 11 runners on base and went 0-for-8 with runners in scoring position.

"That's what we doing the best, leaving people on base," Marlins manager Ozzie Guillen said. "Every time we play good it's because we drive those guys (in). We take advantage. When we don't, we have the result we have tonight."

Bonifacio had three hits, falling a homer shy of the cycle.

The Cubs rebounded from a slow start to move to 13-5 over their past 18 games. They have won nine of their past 11 at home.

Johnson retired nine of the first 10 batters he faced before Castro's home run. Miami's big right-hander responded by striking out the next three.

Johnson was economical until trouble found him in the seventh. Alfonso Soriano singled to lead off and advanced to second on a wild pitch. He scored on Soto's chopper over the head of Hanley Ramirez. Darwin Barney followed with a single to chase Johnson.

"Things were rolling along, I was getting early contact, getting ahead for the most part," Johnson said. "But then you get a chopper and a bloop. Nothing you can really do about it."

Mike Dunn fared no better in relief, surrendering hits to the first two batters he faced, including Baker's double. David DeJesus' sacrifice fly capped the four-run inning.

Johnson was charged with four runs over 6 1/3 innings. He struck out five and walked one to continue an inconsistent season. He gave up seven earned runs in five June starts but has allowed 14 runs in three starts in July.

Guillen was again given a villain's welcome by the home crowd in his return to Chicago. After visiting the mound to remove Johnson in the seventh to a rain of boos, Guillen paused for a moment to banter with fans before disappearing into the visitor's dugout.

Game notes

The Marlins activated RHP Edward Mujica (broken toe) from the 15-day DL. RHP Ryan Webb was optioned to Triple-A New Orleans. .. Cubs OF Jorge Soler will make his minor league debut on Thursday as a DH in the rookie league in Arizona according to GM Theo Epstein. The 20-year-old Cuban prospect signed a 9-year, $30 million contract with Chicago on June 30. ... Mark Buehrle (9-8, 3.13) starts for Miami against Paul Maholm (7-6, 4.33) in the finale on Thursday. It will be Buehrle's first start in Chicago since leaving the White Sox in the offseason for Miami.