(Sports Network) - Slumping lefty Barry Zito hopes to follow the lead of recently successful teammates tonight when the San Francisco Giants head to Land Shark Stadium to open a four-game series with the Florida Marlins.

Zito, in his third season with the Giants since signing as a free agent from Oakland, has lost four straight decisions and six of seven overall this season, continuing a struggle that's seen him go just 22-36 as a Giant.

He was a double-digit winner six times in seven seasons with Oakland, including a career-best 23 wins in 2002.

The 31-year-old Las Vegas native allowed 10 hits and three runs over 6 2/3 innings in his last outing, a 6-2 loss to St. Louis on May 30.

Since his last win on May 8, Zito has surrendered 28 hits and 14 runs in 27 1/3 innings.

Zito is unbeaten in three career starts against Florida, winning a pair of decisions and posting a 3.63 earned run average in 17 1/3 innings.

The Marlins counter with second-year righty Chris Volstad, who'll face the Giants for the first time in his 27th big-league appearance.

Overall pick No. 16 in the 2005 draft, Volstad debuted with the Marlins last season and made 15 appearances, going 6-4 with a 2.88 ERA in 84 1/3 innings.

He started 2-0 in his sophomore season but has stumbled a bit since, losing four of his last six decisions since the end of April.

Most recently, Volstad allowed six hits and three runs in seven innings on May 31 in New York, dropping a 3-2 verdict to the Mets at Citi Field.

In 68 innings, Volstad has allowed just 56 hits and 28 earned runs, walking 21 batters and striking out 54.

The Giants finished off a series with two games in Washington on Thursday and did so in historic fashion, with Randy Johnson picking up career win No. 300 in the opener and Matt Cain pitching six strong innings in the follow-up contest.

Johnson (5-4) allowed just two hits, two walks and an unearned run through six innings in San Francisco's 5-1 decision. The five-time Cy Young Award winner allowed just one baserunner through the first four innings -- a out-out walk to Nick Johnson in the fourth.

The Giants won a rain-shortened nightcap, 4-1, behind six innings from Cain, who improved to 7-1 on the season.

In Florida, Josh Johnson did the expected on the mound and the unexpected at the plate, hitting a go-ahead three-run homer as Florida downed Milwaukee, 4-3, to take three of four from the Brewers.

Johnson (5-1) gave up two runs on five hits with one walk and eight strikeouts, cutting his earned run average to 2.63.

His counterpart, Dave Bush (3-2), was hit by a rocket in the elbow off the bat of Hanley Ramirez in the first, leaving a noticeable bruise. He stayed in to pitch six innings of four-run, seven-hit ball with four strikeouts and a pair of walks.

San Francisco split its six matchups with the Marlins last season, but is 9-4 in the series since the start of the 2007 campaign.