Mariners vs Royals Prediction, Odds, Moneyline, Spread & Over/Under for May 3

Odds updated as of 10:11 p.m.

The MLB’s Sunday schedule includes the Seattle Mariners taking on the Kansas City Royals.

Before checking out the MLB betting lines on FanDuel Sportsbook, we’ve got you covered, in terms of the most important info regarding this game.

Seattle Mariners (16-17) vs. Kansas City Royals (13-19)
Date: Sunday, May 3, 2026
Time: 4:10 p.m. ET
Venue: T-Mobile Park — Seattle, Washington
Coverage: Mariners.TV and Royals.TV

All MLB odds, betting lines and prop bets are available on FanDuel Sportsbook.
Moneyline: SEA: (-142) | KC: (+120)
Spread: SEA: -1.5 (+146) | KC: +1.5 (-178)
Total: 8 — Over: (-108) | Under: (-112)

Mariners vs Royals Probable Starting Pitchers

Probable Pitchers: Luis Castillo (Mariners) – 0-2, 6.35 ERA vs Kris Bubic (Royals) – 2-1, 3.74 ERA

The Mariners will give the nod to Luis Castillo (0-2) against the Royals and Kris Bubic (2-1). Castillo’s team is 1-5-0 against the spread this season in his starts. Castillo’s team is 1-4 this season when he starts and they are the moneyline favorite. The Royals have a 3-3-0 record against the spread in Bubic’s starts. The Royals have not been the underdog on the moneyline when Bubic starts this season.

All MLB win probability predictions and picks are according to numberFire.
Prediction: Mariners win (54.9%)

Kansas City is the underdog, +120 on the moneyline, while Seattle is a -142 favorite at home.

The Royals are +1.5 on the run line against the Mariners. The Royals are -178 to cover, and the Mariners are +146.

Mariners versus Royals on May 3 has an over/under of 8 runs, with the odds on the over -108 and the under set at -112.

Bet on Seattle Mariners vs. Kansas City Royals on FanDuel today!

The Mariners have won in 15, or 51.7%, of the 29 contests they have been named as odds-on favorites in this year.
This season Seattle has been victorious nine times in 16 chances when named as a favorite of at least -142 on the moneyline.
Contests with the Mariners have gone over the total set by sportsbooks in 16 of 33 chances this season.
The Mariners have posted a record of 12-21-0 against the spread this season.
The Royals have won four of the 15 games they were the underdog on the moneyline this season (26.7%).
Kansas City is 2-3 (winning 40% of its games) when playing as a moneyline underdog of +120 or longer.
The Royals have combined with opponents to hit the over on the total 13 times this season for a 13-17-0 record against the over/under.
The Royals have collected a 13-17-0 record against the spread this season (covering 43.3% of the time).

Randy Arozarena leads Seattle in OBP (.377), slugging percentage (.458) and total hits (34) this season. He has a .288 batting average.
Among all qualified batters in MLB, his batting average ranks 41st, his on-base percentage ranks 34th, and he is 57th in slugging.
Cole Young has four doubles, a triple, three home runs and 11 walks. He’s batting .276 and slugging .405 with an on-base percentage of .346.
He ranks 50th in batting average, 72nd in on-base percentage and 94th in slugging in the majors.
Julio Rodriguez leads Seattle in slugging percentage (.400) powered by 10 extra-base hits.
Rodriguez brings a three-game hitting streak into this game. During his last five outings he is batting .318 with three doubles, two home runs and six RBIs.
Josh Naylor has been key for Seattle with 25 hits, an OBP of .285 plus a slugging percentage of .333.

Royals Player Leaders

Bobby Witt Jr. has a team-high OBP (.368) and slugging percentage (.424). He’s batting .288.
Including all the qualified players in the big leagues, his batting average puts him 41st, his on-base percentage is 48th, and he is 77th in slugging.
Maikel Garcia is batting .274 with eight doubles, a triple, three home runs and 13 walks. He’s slugging .436 with an on-base percentage of .344.
Including all qualifying players, he is 54th in batting average, 73rd in on-base percentage and 69th in slugging percentage.
Vinnie Pasquantino is hitting .176 with three doubles, two triples, four home runs and 16 walks.
Carter Jensen has 23 hits to pace his team.

5/1/2026: 7-6 KC (Favorite: Mariners, Spread: -1.5, Total: 7, Favorite Moneyline: -148, Underdog Moneyline: +126)
9/18/2025: 2-0 SEA (Favorite: Mariners, Spread: -1.5, Total: 9, Favorite Moneyline: -120, Underdog Moneyline: +102)
9/17/2025: 7-5 KC (Favorite: Royals, Spread: -1.5, Total: 8.5, Favorite Moneyline: -124, Underdog Moneyline: +106)
9/16/2025: 12-5 SEA (Favorite: Mariners, Spread: -1.5, Total: 8.5, Favorite Moneyline: -136, Underdog Moneyline: +116)
7/3/2025: 3-2 KC (Favorite: Mariners, Spread: -1.5, Total: 7.5, Favorite Moneyline: -120, Underdog Moneyline: +102)
7/2/2025: 3-2 SEA (Favorite: Mariners, Spread: -1.5, Total: 7, Favorite Moneyline: -166, Underdog Moneyline: +140)
7/1/2025: 6-3 KC (Favorite: Mariners, Spread: -1.5, Total: 8, Favorite Moneyline: -138, Underdog Moneyline: +118)
6/30/2025: 6-2 SEA (Favorite: Mariners, Spread: -1.5, Total: 7, Favorite Moneyline: -164, Underdog Moneyline: +138)
6/9/2024: 6-5 SEA (Favorite: Royals, Spread: -1.5, Total: 7.5, Favorite Moneyline: -136, Underdog Moneyline: +116)
6/8/2024: 8-4 KC (Favorite: Mariners, Spread: -1.5, Total: 8.5, Favorite Moneyline: -134, Underdog Moneyline: +114)