The Seattle Mariners (73-64) and the Tampa Bay Rays (67-69) open a 3-game series Monday at George M. Steinbrenner Field in Tampa. First pitch is scheduled for 7:35 p.m. ET. Let’s analyze BetMGM Sportsbook’s MLB odds around the Mariners vs. Rays odds and make our expert MLB picks and predictions for the best bets.

Season series: Mariners 3-0

The Mariners picked up a 3-game sweep over the Rays Aug. 8-10 at T-Mobile Park in Seattle, and that seemed to make the alarm clock go off for Tampa Bay. Since then, Tampa is a respectable 10-7, including a 3-game sweep on the road over the weekend against the Washington Nationals.

In Sunday’s series finale in the nation’s capital, the Rays won 7-4. Tampa Bay scored 6 runs in the top of the second, and it built a 7-0 lead in the top of the third. 2B Brandon Lowe had the big blow in the second, smacking a grand slam, his 28th homer of the season. OF Everson Pereira also drove in a pair of runs.

Seattle avoided a sweep against the Cleveland Guardians at Progressive Field over the weekend. The M’s won 4-2 on Sunday as short ‘dogs (-105) as the Under (8) cashed. LF Randy Arozarena had a 2-run HR, while CF Julio Rodriguez drove in the other 2 runs. SS JP Crawford went 2-for-4 with a pair of runs scored, too.

The Under has cashed at a 3-1-1 clip in the past 5 games for the Rays, although the Over is 4-0-1 in the past 5 home outings. For the Mariners, the Under is 3-1 in the past 4 games, but the Over is 5-2 in the past 7 road contests.

Mariners at Rays projected starters

RHP Luis Castillo vs. RHP Shane Baz

Castillo (8-7, 3.75 ERA) makes his 28th start. He has a 1.28 WHIP, 2.6 BB/9 and 7.9 K/9 through 151 1/3 innings.

Last start: No-decision, 5 IP, 5 ER, 5 H (1 HR), 3 BB, 6 K in 7-6 home loss vs. San Diego Padres Aug. 26Last 7 starts: 1-2, 5.45 ERA (36 1/3 IP, 22 ER), 7 BB, 33 K, 1.51 WHIP2025 road stats: 4-3, 5.04 ERA (64 1/3 IP, 36 ER), 9 HR, 18 BB, 50 K, 1.60 WHIP in 12 starts2025 vs. Rays (1 start): 7 IP, 2 ER, 5 H (2 solo HR), 0 BB, 5 K in 3-2 home win Aug. 8Career vs. Rays: 2-1, 3.16 ERA (37 IP, 13 ER), 6 HR, 11 BB, 35 K, 1.14 WHIP, 8.5 K/9 in 6 starts

Baz (8-11, 5.19 ERA) makes his 27th start. He has a 1.35 WHIP, 3.4 BB/9 and 9.4 K/9 through 144 innings.

Last start: Loss, 6 IP, 3 ER, 3 H, 2 BB, 7 K in 3-0 road setback vs. Cleveland Aug. 26Last 7 starts: 0-6, 8.47 ERA (34 IP, 32 ER), 14 BB, 43 K, 1.65 WHIP2025 home stats: 5-5, 7.06 ERA (66 1/3 IP, 52 ER), 18 HR, 28 BB, 75 K, 1.57 WHIP in 13 startsHas never faced Mariners

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Mariners at Rays odds

Provided by BetMGM Sportsbook; access USA TODAY Sports Scores and Sports Betting Odds hub for a full list. Lines last updated at 7:26 a.m. ET.

Moneyline (ML): Mariners -120 (bet $120 to win $100) | Rays +100 (bet $100 to win $100)Run line (RL)/Against the spread (ATS): Mariners -1.5 (+145) | Rays +1.5 (-175)Over/Under (O/U): 8.5 (O: -110 | U: -110)Mariners at Rays picks and predictionsPrediction

Mariners 7, Rays 5

The MARINERS (-120) are worth playing in the series opener. First off, Seattle has won 6 of the past 7 meetings in this series since June 26, 2024, including a 3-game sweep this season at T-Mobile Park. But, we’re really playing against Baz, who has been atrocious lately, sans for a quality start in Cleveland last time out. He is really teetering on being designated for assignment, that’s how bad he has been. And, pitching at the bandbox Steinbrenner Field has done him no favors this season, either.

If you’re a bit more adventurous, consider MARINERS -1.5 (+145). Again, Baz has been very giving, but be cautious here. While Castillo has decent numbers, he has mostly been a disaster away from home.

OVER 8.5 (-110) is easily the best play in this series opener, so go rather aggressively on this one.

The Over is 5-2 in the past 7 games on the road for the Mariners, and, again, Castillo has been knocked around on the road. Baz has been knocked around most everywhere lately, but especially so in Tampa this season. And, the total has gone high at a 4-0-1 clip at home for the Rays.

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