It was always expected that the San Francisco Giants would struggle offensively this year. They weren't a great offensive team a year ago on the way to winning their second World Series in three years. The Giants won largely because of their pitching -- well, NL MVP Buster Posey certainly deserves some credit -- and it was presumed that group again would have to carry the team in 2013 after it didn't add any big bats via free agency or trade this offseason. However, the Giants enter Monday's series opener in Arizona at 13-12 and on an MLB-high five-game losing streak largely because their pitching is struggling. The team ERA of 3.71 is ninth in the National League, and San Francisco's 13 quality starts ranks 10th in the NL. No pitcher has struggled more than Matt Cain, last year's NL All-Star Game starter.

The Diamondbacks have been a surprise and are tied with Colorado atop the NL West at 15-10. They made the risky choice of trading super-talented-but-enigmatic outfielder Justin Upton to Atlanta this offseason, and Upton has been arguably the NL MVP thus far. Arizona's main major-league return was third baseman Martin Prado, and he has struggled with a .208 average. But, really, the Snakes did it to add depth to the organization, also getting young pitcher Randall Delgado and three other prospects. The Diamondbacks have a pretty no-name lineup now, but it ranks No. 5 in the NL in runs and No. 4 in average.

Giants at Diamondbacks Betting Story Lines

Cain (0-2, 6.59) gets the call in the opener for San Francisco.  Since pitching six scoreless innings in his first start of the season against the Dodgers, his ERA is 8.34. He's had two starts already this year where he has allowed seven earned runs and also has allowed six combined homers. Last time out he got a no-decision against Arizona, allowing four runs and five hits in six innings. This is the longest Cain has gone winless to begin a year since his third full season in 2008. Maybe it's a good thing this game is in Phoenix. Cain has an 11.17 home ERA this season and 4.26 on the road. He's 13-6 with a 3.38 ERA in 181.0 innings against Arizona in his career. Paul Goldschmidt hit a two-run homer in that last game against Cain and is batting .250 in his career against Cain. Red-hot Gerardo Parra, who has a career-best 13-game hitting streak (longest active run in NL), is hitting .220 in his career against Cain.

Arizona goes with Ian Kennedy (1-2, 4.70). He pitched well in his last start but got a no-decision against the Giants, allowing one run and four hits in six innings April 24. It was Kennedy's second straight quality start. Kennedy is 6-2 with a 2.33 ERA in 14 career starts against the Giants. Posey is hitting .348 in 23 at-bats against Kennedy; Posey is also hitting .400 (12-for-30) during a season-best nine-game hitting streak. Brandon Belt is the only Giant with a homer against Kennedy. 

Diamondbacks manager Kirk Gibson gave Prado the day off Sunday, his first all year, but he should be back in the lineup. Prado is hitting .136 since April 12 and has one hit in his last 22 at-bats. Arizona has one of the most exciting young shortstops in baseball in Didi Gregorius, but he's out this week after being hit in the head with a fastball on Saturday and suffering a concussion. Gregorius was hitting .407 with two homers in 27 at-bats. Cliff Pennington will man shortstop while Gregorius is out. Pennington is hitting only .184 in 23 games.

Giants at Diamondbacks MLB Betting Odds and Trends

At WagerWeb, Arizona is -111 and San Francisco -109 with the total at 8. The Giants are 13-12 “over/under” (7-6 on road) and 9-16 on the runline. The Diamondbacks are 8-16-1 O/U (4-8-1 at home) and 14-11 on the runline.

The Giants are 4-0 in their past four road games vs. a team with a winning record. They are 2-6 in their past eight against a righty starter. San Francisco has lost four straight as a dog and six straight on the road. They are 11-3 in Cain's past four starts as a road dog. The Giants are 0-5 in Cain's past five starts. Arizona is 5-1 in its past six vs. teams with a winning record. Arizona is 1-8 in its past nine Monday games. The Diamondbacks are 9-1 in Kennedy's past 10 starts when their opponent allows at least five runs in its previous game. The Snakes are 5-1 in Kennedy's past six series opening starts. The over is 5-1 in Cain's past six starts vs. teams with a winning record. The over is 5-2 in Cain's past seven starts overall. The under is 7-1 in Arizona's past eight series openers. The under is 5-1 in Kennedy's past six series openers. Arizona is 8-0 in Kennedy's past eight starts against the Giants. The under is 5-2 in Cain's past seven starts at Arizona.

Giants at Diamondbacks Picks and Betting Predictions

You'd have to say the Giants are due as they have lost six straight on the road, their longest skid away from home since early in the 2009 season. If it goes extra innings, you have to like Arizona's chances as it is 6-0 in extra frames this year. Eighteen of Arizona's 25 games have been decided by two runs or fewer. I think Cain will snap out of things sooner rather than later, but Kennedy hasn't lost to the Giants in nine straight starts. Take Arizona and the under.

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Read more articles by Alan Matthews