The Seattle Mariners hope to extend a five-game winning streak by picking up a sweep over the Arizona Diamondbacks this afternoon.
Bryce Miller has been impressive since returning from injury, and my Diamondbacks vs. Mariners predictions explain his slider will neutralize the visitors while Merrill Kelly has a rough day.
Here are my MLB picks for May 31.
Who will win Diamondbacks vs Mariners today: Mariners -1.5 (+155)
After a brutal start to the season, Merrill Kelly’s posted four consecutive quality starts with a .237 wOBA — but I’m not convinced.
I’m not buying it when a career ground-ball pitcher allowed fly balls (49.4%) and hard hits (41.4%) at the rate he did in those starts — especially not while posting a 0.60 GB/FB ratio.
The Seattle Mariners rank sixth in HR/FB rate (14.6%) over the past two weeks with a 0.88 GB/FB ratio.
Kelly ranks in the bottom percentile in both barrel rate and xERA. I’m backing the Mariners to punish him and cover up to +130.
COVERS INTEL: Kelly’s fastball (7.9%) and cutter (11.1%) putaway rates have plummeted from last season, while Seattle’s 45.3% FB% against those pitches is the league’s seventh-highest this month. 
Diamondbacks vs Mariners Over/Under pick: Under 7.5 (-114)
While I’m expecting the Mariners to win easily, I am taking the Under to -120.
Bryce Miller has added 2 to 3 mph onto all of his pitches and has tripled his slider usage from a season ago. That breaking ball is generating a 43.3% whiff rate thanks to an additional 2.6 inches of induced vertical break.
That is a devastating equalizer against the Arizona Diamondbacks, who have a league-leading 48.2% pull rate over the last two weeks.
Seattle’s pen has been outstanding this month, ranking fourth in xFIP (3.56), sixth in K% (24.4%), and sixth in wOBA (.290).
- ML/RL bets: 9-12, -3.94 units
- Over/Under bets: 13-8, +4.28 units
Diamondbacks vs Mariners odds
- Moneyline: Diamondbacks +133 | Mariners -138
- Run line: Diamondbacks +1.5 (-156) | Mariners -1.5 (+150)
- Over/Under: Over 7.5 (+100) | Under 7.5 (-104)
Diamondbacks vs Mariners trend
The Seattle Mariners have covered the run line in four of their last five games (+4.80 Units / 96% ROI). Find more MLB betting trends for Diamondbacks vs. Mariners.
How to watch Diamondbacks vs Mariners and game info
| Location | T-Mobile Park, Seattle, WA |
| Date | Sunday, May 31, 2026 |
| First pitch | 4:10 p.m. ET |
| TV | DBacks.TV, Mariners.TV |
| Diamondbacks starting pitcher | Merrill Kelly (5-3, 5.25 ERA) |
| Mariners starting pitcher | Bryce Miller (1-0, 2.25 ERA) |
Diamondbacks vs Mariners latest injuries
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Odds are correct at the time of publishing and are subject to change.
Not intended for use in MA.
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