3 Best MLB Bets and Player Props for Mariners at Diamondbacks on Monday 6/9/25

Even within a single MLB game, you've got countless betting markets to choose from.

Which ones stand out today as the Seattle Mariners take on the Arizona Diamondbacks

We're going to run through my favorites in FanDuel Sportsbook's MLB betting odds. You can also check out FanDuel Research's MLB player prop projections if you want a glimpse at projected strikeouts, home runs, and more.

Now, let's dig into the best bets for this game.

Betting Picks for Mariners Diamondbacks

Diamondbacks -0.5 First 5 Innings Run Line (-130)

The Mariners are 1-5 over the last six, and the Diamondbacks come off the losing end of a series sweep against the Cincinnati Reds. For Monday's series-opening game, Arizona should have the clear advantage on the mound.

Starting with Seattle, Emerson Hancock will make his 11th start, and he touts a 5.19 ERA, 4.40 SIERA, and 4.21 xFIP. The Diamondbacks have scored the fourth-most runs paired with the fifth-highest batting average against right-handed pitching. Hancock's most-used tools are his sinker (36.8%), changeup (23.5%), and four-seam fastball (23.5%).

Arizona is in the top half of runs above average against all three pitches, including the ninth-highest mark against sinkers and second-highest when seeing four-seam fastballs. The concerns go on as Hancock is allowing 1.61 HR/9, and the D-backs have the fourth-highest home run percentage.

Meanwhile, Merrill Kelly has performed well for Arizona, sporting a 3.43 ERA, 3.51 SIERA, and 3.38 xFIP. He comes off a seven-inning showing while allowing only one hit. With the 10th-lowest batting average, Seattle leans on power hitting by smacking the 6th-most home runs per game. Kelly gives up 0.95 HR/9, which is a shade under the league average of 1.02.

The D-backs have a clear advantage for the starting pitcher matchup. Plus, Arizona is already the better batting squad, scoring the 6th-most runs compared to the Mariners with the 14th-most.

Corbin Carroll to Record 3+ Total Bases (+110)

Backing one of the Diamondbacks' hitters should bring good value against Seattle. We don't have to look far as our MLB DFS projections have Ketel Marte and Corbin Carroll projected with the most fantasy points for today's slate (14.8). Between the two, Carroll's matchup is drawing more attention.

Similar to Marte, Carroll is putting up his best numbers against righties with a .270 batting average compared to .235 when facing southpaws. Pitch usage is where Carroll is a step ahead of Marte. He is hitting .237 against sinkers, .278 against changeups, and .359 when facing fastballs. The mark against sinkers is concerning, but Carroll bats .310 against the pitch across his career -- suggesting positive regression. Backed by solid numbers against Hancock's most-used pitches, we have an angle for success.

We mentioned Hancock's struggles against slugging this season, and Carroll is in the 95th percentile of barrel rate, 87th percentile of hard-hit percentage, and 89th percentile of bat speed. Reaching at least three bases will heavily lean on extra-base hits, and Carroll's projections for Monday are nearly are on par with baseball's best sluggers. For example, Carroll is forecasted for 0.23 doubles and 0.27 homers, and Shohei Ohtani carries 0.23 doubles and 0.28 big flies for tonight.

The Mariners' bullpen also has the 11th-highest SIERA, boosting Carroll's chances of reaching at least three bases.

Merrill Kelly Over 5.5 Strikeouts (-106)

Kelly is gearing up for a favorable matchup, and it goes beyond just a deep start. He's been on a roll in the strikeout category of late by reaching six Ks in six consecutive starts. After logging 7.5 Ks per game over the previous six, over 5.5 strikeouts is bringing excellent value.

Seattle has the eighth-highest strikeout percentage and log the fourth-most Ks per game. This hasn't slowed, either, for the Mariners have totaled double-digits strikeouts in three of the last five.

Kelly's strength when stacking Ks has been his 30.2% chase rate (70th percentile). Seattle is also in the top half for the highest chase percentages, once again elevating one of Kelly's strengths.

Ultimately, I'm expecting another strong start from Kelly. If that's the case, over 5.5 Ks is well within reach considering the matchup on hand.

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The above author is a FanDuel employee and is not eligible to compete in public daily fantasy contests or place sports betting wagers on FanDuel. The advice provided by the author does not necessarily represent the views of FanDuel. Taking the author's advice will not guarantee a successful outcome. You should use your own judgment when participating in daily fantasy contests or placing sports wagers.