Guardians vs. Diamondbacks Prediction, Odds, Probable Pitchers and Prop Bets for Monday, Aug. 18

The Guardians could be a sneaky upset bet on Monday.

Cleveland Guardians designated hitter Kyle Manzardo is a great prop target on Monday. / David Richard-Imagn Images

The Cleveland Guardians are 3.5 games out of a playoff spot in the American League, but they have a chance to make up some ground in a favorable early-week series against the Arizona Diamondbacks.

Arizona is likely going to miss the playoffs in the NL this season, as it is five games under .500 and traded away several key pieces at the trade deadline. As a result, the D-Backs are 6.5 games out of the final wild card spot in the NL. 

The best betting sites still have Arizona favored in this matchup on Monday, as Zac Gallen (5.31 ERA) is on the mound for the home team against Cleveland’s Gavin Williams (3.38 ERA). Williams’ advanced numbers are a little shaky in 2025, but the Guardians have fared pretty well in his starts.

Can they keep that going with every win meaning more down the stretch of the regular season?

Here’s a breakdown of the odds, players to bet on in the prop market, and my prediction for this series opener on Monday night. 

Guardians vs. Diamondbacks Odds, Run Line and Total

Odds via DraftKings Sportsbook

Run Line

• Guardians +1.5 (-194)
• Diamondbacks -1.5 (+158)

Moneyline

• Guardians: +104
• Diamondbacks: -126

Total

• 9 (Over -105/Under -115)

Guardians vs. Diamondbacks Probable Pitchers

• Cleveland: Gavin Williams (7-4, 3.38 ERA)
• Arizona: Zac Gallen (9-12, 5.31 ERA)

Guardians vs. Diamondbacks How to Watch

• Date: Monday, Aug. 18
• Time: 9:40 p.m. EST
• Venue: Chase Field
• How to Watch (TV): ARID, CLEG
• Guardians record: 63-60
• Diamondbacks record: 60-65

Guardians vs. Diamondbacks Best MLB Prop Bets

Guardians Best MLB Prop Bet

• Kyle Manzardo to Hit a Home Run (+380)

Earlier today, I shared in SI Betting’s best home run picks – Daily Dinger – why Manzardo is a solid value bet against Zac Gallen: 

The Cleveland Guardians are still in the mix for a playoff spot in the AL, and they’ll look to put up a big number against Arizona Diamondbacks starter Zac Gallen on Monday.

Gallen has allowed 24 home runs in 25 starts in the 2025 season while posting a 5.31 ERA. That makes him an easy pitcher to fade in this market, especially against some left-handed batters, who are hitting .283 against Gallen this season.

Enter: Kyle Manzardo.

The Guardians slugger has 21 home runs this season, 17 of which have come against right-handed pitching. He’s also homered three times over his last 10 games, posting a .276 batting average and a 1.057 OPS during that stretch.

At nearly 4/1 odds, he’s worth a look against Gallen on Monday night. 

Guardians vs. Diamondbacks Prediction and Pick

Usually, a starting pitcher with Williams’ advanced numbers would be someone that I’d stay away from, especially when placing a moneyline bet.

Williams has an expected ERA of 4.23 and ranks in the fifth percentile in walk percentage this season, but I think he has the edge over Gallen, who has a 4.87 expected ERA and has yet to get on track in 2025.

Gallen has allowed four or more runs in 14 of his 25 starts this season, and he has a shaky bullpen backing him up that ranks 27th in ERA (4.90). 

Meanwhile, the Guardians are fourth in MLB in bullpen ERA (3.58), and I trust them to back up Williams if he’s able to leave the game with the lead. Williams has given up less than four earned runs in 19 of his 24 outings this season.

Cleveland has a shaky record when he’s on the mound (11-13), but I can’t trust Gallen in 2025. The former All-Star has a 1.35 WHIP and ranks in the 25th percentile or worse in expected batting average against, barrel percentage, and hard-hit percentage this season. 

Pick: Guardians Moneyline (+104 at DraftKings)

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Odds refresh periodically and are subject to change.

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